I enjoy writing spells with the Buffy magic system.  You can do just about anything you can imagine.  Here are some I've written for my games, or just for the fun of writing them.

Barrier of Koranos
Quick Cast: No (at least not exactly)
Power Level: 5
Requirements: Specially prepared parchment, ink made from a variety of expensive substances, and an alchemically prepared soot made from burning certain woods and herbs mixed with other chemicals.

Effect: Casting the Barrier of Koranos is a slow process. Each roughly two-hour ritual results in the creation of one card covered in black soot and sparkling golden ink. The cards are anchors for a protective spell. Whenever they are placed in a perfect geometric shape with an odd number of sides, up to thirteen, from three to thirty paces apart, they immediately create a mystical shield.

The shield has can take 80 points of damage, and has an armor value of 10 +2 per card beyond the third. So A five-point barrier would have an armor rating of 14.

The Barrier cards are consumed by arcane energies in the casting of the spell.

Call the Dragon's Breath
Quick Cast: No
Power Level: 6
Requirements: A ritual taking an entire day (12 hours), during which time the caster sacrifices something of great personal value. The sacrifice can be a possession, a person, a supernatural power, or even an ideal. It is up to the Director to determine if the sacrifice was sufficient. If not, the spell is still cast, but cannot succede. If the caster gets enough success levels, the spell is miscast. (see below for why this is a VERY bad thing)

Effect: This powerful, but ancient spell is used rarely, even by those few who know it. The Dragon is a powerful and terrible force, and exacts a high price.

The Dragon's Breath fills the caster, granting several benifits. Foremost among these is a Power Boost of +10. Further, the Power Level of all spells the caster wishes to cast is reduced by half (round up), for purposes of success. The effect lasts for as many hours as the caster's boosted Sorcery level, or until he exhausts his Sorcery with multiple castings. Additional Power Boosts will work as normal, further extending the duration of the Dragon's Breath.

Casting this spell is very dangerous. If the casting fails, the caster takes life point damage equal to his own Willpower x 3, and is knocked unconscious until the damage is healed. Regeneration does not speed the recovery of this damage, but various forms of magical healing might.

Succeding can be even more dangerous. If the roll succedes, but the power level is not met, the caster dies, rapidly aging and decaying to nothing over the course of a day as the Dragon absorbs all his life force. There is no way to reverse this process.

If the caster is successful, at the end of the Dragon's Breath, he still suffers a Side Effect as though he had miscast the most powerful spell he used during the duration (using the full power level, not the half one). Most frequently, the result is a coma of varying length, but the Dragon is capricious. If the caster has not completely expended the Dragon's Breath, every bonus point of Sorcery he has left is added to the roll.

note:Sweet Jesus, this is a powerful spell as written. I thought the power level would be higher. It could be lower, if I decide the sacrifice is more of a rare ingredient. I made it just -1, because while you probably don't want to sacrifice something you love, it's readily available.

Oracle's Benediction (type)

Quick Cast: No
Power Level: 4
Requirements: An Oracle (Someone with psychic powers who knows this spell)  The supplicant must make an offering to the gods, burning something of value in front of the Oracle.  At the GM's option, an
insufficient offering can cause the spell to fail or even backfire.  The Oracle then meditates and chants a ritual for a several minutes before pronouncing the Benediction, which is a cryptic phrase vaguely related to the purpose.  Hearing the phrase is what transfers the favor of the gods.  If the supplicant can't hear the Benediction, the spell automatically fails.  (Writing on a slate or sign-language counts, so long as the supplicant witnesses the actual act of writing or signing in
person.  No email or teleconferences.  The gods are big on personal contact.)

Effect: There are several seperate Benedictions, each counting as a seperate spell.  (Of course, once you know one, you can probably develop the others through research.)  Their effects are similar, but each with a different focus.  The basic effect is that the supplicant is granted supernatural insight and divine favor, making his efforts more successful than they'd otherwise be.  In down-and-dirty game terms, the supplicant gets temporary levels of Good Luck that can only be spent in circumstances befiting the particular Benediction, and are spent automatically whenever the Benediction would come into play.  (The player gets to choose how many points, however, so long as he spends enough to get at least one SL on the relevant test or just barely win an opposed test)

The Oracle's Benediction provides Good Luck equal to twice the Success Levels generated.  These points are never recovered after they're spent.

Benediction of Protection: Provides help to keep the supplicant alive. He can add Luck points to his defense tests until they run out.  These points are almost always automatically spent, but they're spent after damage is generated.  They kick in retroactively to protect the supplicant from any wound that would cause half or more of his current Life Points in damage.  Besides dodge tests, the Benediction will protect the supplicant from other forms of potentially fatal harm.  The GM can choose how many luck points are required to avoid something you don't normally get a roll to avoid.

Benediction of Success: Provides the supplicant with aid in a specific task, which must be stated at the time of casting.  Tasks must be fairly specific, or else the divine favor gets absorbed fairly quickly. Suitable tasks would be "to find the golden fleece," or "to conquor Thrace."  "To win the lottery" works, too, but there's only so much the gods can do.  You'd pick the best random numbers you could, but your chances of actually winning would still be pretty low.  "To create the best possible [something or other]" would also be good.  You'd end up burning all your Luck on an Art or Mr. Fix-It test, but you'd be able to excede your usual skill limits if the GM is imposing those.  Divine inspiration is like that.

Benediction of Aphroditie's Favor: Provides help in the wooing of a specific individual.  You get Good Luck points to spend on Influence tasks with that person.  With the GM's permission, you might also be able to spend them like Drama Points for "Plot Twists" like guessing the person's favorite song or picking a resturant they really like.  I'd suggest a sliding scale.  The first coincidence costs 1 point, then one additional point per coincidence.  (What, you expect the gods to do EVERYTHING?)

A Benediction lasts for a number of weeks equal to the SL generated.  After that, it fades and any further points spent are lost.

A given supplicant can only be under the effects of one Benediction at a time, and must wait a full lunar month between Benedictions.  Breaking this restriction invites the scorn of the gods, which comes in the form of all benedictions active upon the supplicant inflicting Bad Luck points instead of Good Luck.  Sucks to be you if that happens, so don't get greedy.

Quintra's Adept Recal
Quick Cast: Yes
Power Level: 1

This spell requires the tools of a true adept, for instance a master thief's lockpicks, or a master swordsman's favored blade. High skill is not enough. The tools must have been used for some time by a truly legendary master. The tools in question must be in working condition, and the adept in question must be dead.

By focusing his will, and chanting a prayer to Thoth, the Sorcerer (Sorcery 3 minimum) may call upon the skills of the former adept. Thereafter, until the spell fades (after several hours), anyone who uses the bespelled tools in their intended way gains a skill bonus equal to the number of extra success levels the Sorcerer rolled.

A given tool (or set of tools in the case of something like lockpicks) may only ever be enchanted in this way once. At the end of the spell's duration, the affected item(s) rapidly sucumb to decay, collapsing into dust in a matter of seconds. No force on earth can prevent this destruction.

Substitutary Locomotion
Quick Cast: Yes
Power Level: 3
Requirements: A half-hour ritual in which the caster sits within a circle inscribed with the Star of Astaroth, surrounded by candles while meditating and chanting. For Sorcerers, a little concentration and the words "Treguna Mekoides Tracorum Satis Dee"

Effect: This spell summons up ephemeral spirits that will inhabit clothing and animate it. The spell is somewhat unpredictable. The animated clothing, which can be anything from normal clothes to suits of armor, will behave according to its nature, in general accordance with the will of the caster. Animated army uniforms would move with military precision. Animated clown suits would act like clowns. About ten such sets of clothes can be animated. Available clothing will always group itself by theme, and create complete "outfits" if possible. So, for instance, if you had a set of football pads, shoes, helmet, pants, and jersey, you'd get one phantom footbal player, not five.

They will not harm the caster, and will generally be as helpful as whatever they're animating could be. They have Physical stats equal to the caster's mental stats and skills equal to his Sorcery - but cannot perform complex actions like computer programming or surgery.

They "live" for the duration of the spell (one minute per success level) or until they are destroyed (see "Breaking Stuff"). The duration can be extended an extra minute per SL with a Will roll at -1 for every extention.

Therion's Threshold Seal
Quick Cast: Yes
Power Level:5
Requirements: A chalky dust made from the ashes of a funeral pyre (or a crematorium fire) and various healing herbs - used to trace a magical diagram on the recipient's forehead or torso. The diagram is traced while the caster recites a chant to ward away the spirits of death.

Effect: The recipient of Therion's Threshold Seal must be a living, flesh & blood being who is in need of making Survival Tests and/or has 0 or fewer Life Points. When the spell is cast, the recipient is bestowed with ten levels of Hard to Kill, including the 30 Life Points.

The benifits only last as long as the recipient is relatively still. If he engages in any sort of strenuous activity (pretty much anything requiring the rolling of dice), the Threshold Seal fades at the rate of one point of Hard to Kill (along with its 3 Life Points) per minute. Fortunately, the spell leaves the recipient listless and tired. He has to make a Willpower doubled roll to get up and move around at all, and has to make another one every time he stops and wants to start again.

The Seal lasts for one hour per success level, unless it is broken beforehand.