Cold Iron Mana Point System
Cold Iron uses a mana point (or spell point) system (to add a little bit of confusion, there actually are both mana points and spell points...). Every character has mana points (MP). Starting characters generally start with about 20 MP, possibly 30 for mages (and theoretically as high as 38). Clerics get both MP and SP. MP increases slowly with level (mages add twice their level, clerics add their level, non-spell casters have a passive or defensive magic level which is added to MP).
MP recovery is at a rate of 1/6 current MP per hour. This is a continuous function just like bank interest (which means if we need to know exactly how many MP you have, or how long it will take to recover, we need to whip out the calculator - generally an estimate is close enough, or enough time passes that we don't need to worry about it).
Clerics regenerate MP slower (usually at 1/12), with the excess being donated to their deity. However, in exchange they get spell points, which come back during their daily prayers. Spell points follow a formula that is geometric with level, and is based on the cleric's faith attribute.
One of the things I think is really cool about the system is that even when a character's MP is at full, the regen is still pumping out MP. There are spells that cost a few MP per hour, which can be maintained by this excess MP.
Higher level mages have a MP storage focus, which (here's more math) is essentially a leaky bucket. It is charged up (using the same forumula as charging a capacitor) with MP regen.
Most offensive spells cost 1 or 2 MP to cast. Additional MP up to the caster's level may be used to increase success chance, or reduce save (unfortunately, the system does depend on two chance adjustment resolution rolls per offensive spell, one for success, and one for save or for to hit). Energy spells (which are single target and require a to hit roll) cost 1 MP per die, with the die getting bigger as the spell level increases, energy spells can't crit. Magic missile costs 1 MP, requires a to hit, and can crit. There are a variety of defensive spells. Energy resistance spells cost MP based on how much damage they absorb (with higher level spells being more efficient). There is a temporary hit point spell which absorbs a 1/2 or more of the damage received, and costs MP based on how much gets through (thus it also gets more efficient at higher levels).
A lot of utility spells (see invisible, detect magic are two common ones) cost 1+2/hour. Light costs 1/30watts + 1/30watts/hour. These spells are common to be maintained.
Attribute boosting spells cost 2/+1 + 2/+1/hour (and do get more efficient at higher levels). A caster can stack these spells (though there are maximum attribute caps) as long as he has enough MP.
Enchant weapon has a geometric cost based on the bonus granted and is capped by caster level.
Non damage spells include demoralization which reduces the targets offensive ability (and may cause them to run away), entrancement (a parking spell, though the target recognizes direct threats so you can't just take the guy out like D&D's hold person), cluminess, weakness for the common ones. Sleep, paralysis, disintegration, and death are high level spells.
Higher level spells take longer to cast (spells higher than 1/2 caster level take 2 rounds to cast), are harder to succeed with, and are easier to save against. This tends to mean the low level spells are the most common (plus I've never actually run a game to a high enough level to see the "save or die" spells).
There's a lot more to the magic system like counters, dispelling, magic protection spells (there's a lot of defense, though anti-magic shell was taken away - Mark tells me that when it went away, people were concerned for fighters, but it turned out it was mages who got plastered). The spells mostly allow the mage to support the fighter, though the mage's contribution can not be discounted - the battles last week with the skeletons turned very heavily on how successefull the magic was. The key for me is that the fighter and the mage need to cooperate, rather than in D&D where it seemed like the purpose of the fighters was to screen the mages while they did the killing.
Oh, I should also comment on how the mage prepares spells. The mage gets a number of memorization points that increase geometrically with level, and are based on talent. A spell costs it's level to memorize, but lower level versions of the spell are included for free (so if you know Fireball VIII, an 8th level spell, you also know Fireball II, Fireball III, Fireball IV, Fireball V, Fireball VI, and Fireball VII). Mages can also cast any spell from their books (usefull for casting light before entering a cave). Clerics get more memorization, but don't have books. Clerics have a more limited spell list (based on their deity's domains), and get some spells earlier, and some later (they particularly get healing earlier than mages, and much more efficient).