One thing to note: You can't always trust the spell descriptions. It is not safe to assume the spell behaves as expected unless you actually test it. Also, don't assume spells work the same way they do in other AD&D based RPGs.

One note about summons: Only one summon spell can be in effect at a time. If you try to cast another, the spell will fail.

Note that all spells were tested outside of combat

Preserver spells:

Enlarge: Doesn't cause any obvious change. In particular, doesn't change Strength or displayed damage amounts

Antimagic Shell: Doesn't seem to do anything outside of combat. There's no icon to cancel its effect.
Globe of Invulnerability: This affects healing spells, so be careful.

Reincarnation: Revives with full HP and no Constitution loss, but race changes randomly (see the reincarnation topic for details) This spell can even be cast during combat. (Who needs a divine healer when you can just keep Reincarnating dead characters?)

Tenser's Transformation: No visible change on the stat screen, except for the doubling of current HP. Canceling the effect lowers HP to its normal maximum (note that you can still heal by casting the spell and canceling it). Does not prevent the use of psionics.

Delayed Blast Fireball: Is actually a stationary area attack. Anyone entering the spell area (including innocent NPCs) after the spell is cast takes damage. Does not block line of sight (unlike similar spells)

Mordenkainen's Sword: Is a summon (like in Baldur's Gate 2), not a weapon creating spell (like in Dungeon Hack or Icewind Dale)

Divine spells:

Altruism: Works just like Lend Health.

Dust Devil: Is missing from the manual, but is in the game. Will fail if there is another summon alive.

Spiritual Hammer: Creates a ranged weapon that gets damage bonus from Strength and number of attacks from Fighter levels. (Could be very useful for a Half-Giant Fighter/Cleric) Note that this is different from Shattered Lands (where it creates a melee weapon). Actually testing this spell against a summoned dust devil, I can't seem to make ranged attacks for some reason. (Seems like a bug to me.)

Bramblestaff: Does not work at all. The staff appears in your inventory, but does not appear as an equipped weapon.

Air Lens: Does not appear to do anything outside of battle

Conjure Lesser Elemental: Is not in the game; this is the one spell (that I am aware of) from Shattered Lands that is absent in Wake of the Ravager.

Magma Blade: Does not do an extra 2-12 damage. Disappears after one hit (but the spell effect is still there.)

Rainbow: When cast, current HP is reduced. Can attack 4x per round. No strength bonus. Edit: The loss of HP can kill the caster. Also, spell only lasts one round, so if cast during combat, will wear off before you actually get to attack.

Fire seeds: Is not a weapon-creating spell. It actually is an area attack, similar to Produce Flame or Fireball (though the area is pretty small); however, you get to fire multiple attacks with one casting (at least 2, description says 4).

Heal: Is actually 1e Heal, which heals all but 1d4 hit points. (Why they implemented 1e heal in a 2e game I don't know, especially since 2e Heal is slightly easier to implement and takes slightly less code.)

Heartseeker: Actually creates an arrow that can be traded. Canceling the spell will get rid of heartseeker arrows in the caster's possession, but not those held by other characters, allowing you to stock up on them.

Sunstroke: Air clerics can use this spell. (This makes this spell the only spell, to my knowledge, that is both Cosmos and in another sphere (but see Sunray). It's also the only 6th level Air spell.)

Water of Life: Acts like Heal. (Again, this is 1e heal, not 2e heal, so it doesn't *quite* fully heal the target.) Does not harm the caster in any way.

Sunray: Also in both Air and Cosmos.

Edit 1: Add Mordenkainen's sword and note about other games.

Edit 2: Add in information about Air Spells and note about the summon limit

Edit 3: Add note about Rainbow: It can kill the caster if she is low on health, so be careful! (At least, unlike Spiritual Hammer, the spell works properly.)

Edit 4: Added notes about Magma Blade and Rainbow, which fail to function as they are supposed to. (Rainbow's duration is too short.)

Edit 5: Bramblestaff is also broken. (The developers really messed up when it came to weapon creation spells. Only Flame Blade and Shilelah work properly.)

One more observation: If you use the "All Spells" cheat, you will get access to 8th and 9th level mage spells. Some work sensibly (Meteor Swarm is basically 4 separately targeted fireballs; Time Stop seems to work, except that your movement doesn't reset between attacks), while some don't (Can't seem to create a Prismatic Wall; Prismatic Sphere crashes the game).

Edit: One other thing: Time Stop will work, but it will never wear off, making the spell basically an "I Win" button.

I created a Prismatic Wall with a character who actually had Preserver levels.

The 8th level Bigby's spell is actually summons a Magma Golem. Strange.

Prismatic Sphere still crashed the game, however, so don't use that spell.

I suspect the game was intended to have a higher level cap, but something happened during the game's development (time pressure, maybe?) so they had to scrap that. At that point, they had already decided which level 8+ spells to implement and had even started implementing them, but they didn't finish some of the spells. Hence, some of them (Time Stop and Prismatic Sphere) were left in an unfinished state, and the developers just made sure the player couldn't obtain those spells under normal circumstances. The Bigby's Hand spell summoning a Magma Golem is probably because that monster slot was originally intended to contain the summoned hand, but that summon was never created and a different monster was placed in the slot. Time Stop had started to be implemented, but the code was incomplete, resulting in the behavior I mentioned above. Prismatic Sphere likely wasn't implemented at all, or the implementation had a bug that was left in, or it referred to an asset that was removed with nothing put in its place.