Here are the Enemy Skills, their effects, how much MP they use, and which enemies you can learn them from. They are shown in a general order of appearance. (They won't necessarily show up in this order, but the order below is pretty representative).
Matra Magic - Non-elemental damage to all enemies - 8MP
Mechanical monsters (Midgar Area), BullMotor (Gold Saucer Prison), Death Machine (Junon Highways)
Lv4 Suicide - Inflicts Critical Status and uses Mini on opponents with levels in multiples of 4 - 10MP
Mu (Grasslands Area), Trickplay (Icicle Area)
Flame Thrower - Fire elemental damage to one enemy - 10MP
Ark Dragon (Mythril Mines)
Laser - Reduces one opponent's HP by half - 16MP
Death Claw (Gold Saucer Prison), Dark Dragon (Northern Cave)
Frog Song - Uses Toad and Sleepel on one opponent - 5MP
Touch Me (forest NorthWest of Gongaga Reactor), Toxic Frog (Temple of the Ancients)
Big Guard - Uses Barrier, MBarrier on all allies
Beach Plug (beaches near Gongaga Reactor)
Death Sentence - Causes Doom (a timer counts down from 60 to 0. At 0 the afflicted ally/opponent dies) - 10MP
Sneaky Step (Cave of the Gi), Gi Spector (Cave of the Gi), BoundFat (Corral Valley)
Trine - Lightning elemental damage to all enemies - 20MP
Materia Keeper (Mt Nibel), Stilva (inside Gaea's cliff). This Enemy Skill is not used by any enemies in Disc 3. It can only be learnt in Discs 1 and 2.
Beta - Fire elemental damage to all enemies - 35MP
Midgar Zolom (Marshes near Grassland Area)
Aqualung - Water elemental damage to all opponents - 34MP
Jenova-LIFE (Forgotton Capital). If Jenova-LIFE doesn't use this attack as a first attack, she (it?) will probably not have enough MP to use it later in the battle. Since it is impossible to manipulate her, you will have to restart the game if she doesn't use it as the first attack. However you can also learn this Enemy Skill from Harpy (Gold Saucer Area).
Magic Breath - Fire, Ice, Lightning elemental damage to all opponents - 75MP
Stilva (inside Gaea's cliff), Parasite (Northern Cave)
Bad Breath - Uses Poison, Confu, Sleepel, Silence, Small, Frog on all opponents - 58MP
Marlboro (inside Gaea's cliff)
White Wind - Restores the amount of HP the user has to all other allies and restores normal status. (So, if the person casting White Wind has 139HP, all other allies and the person casting the Enemy Skill will receive 139HP) - 34MP
Wind Wing (Whirlwind Maze) I could never get this Enemy Skill to show up on the menu after Manipulating it, so use Lv4 Suicide on it (to give it Critical Status - of course this only works if its level is a multiple of 4). Now immediately Confuse it, and it will use White Wind to try and heal itself of the Critical Status, and will most probably use the White Wind on your party. You can also learn this Enemy Skill from Zemzelett (Junon Area). White Wind does show up on the menu of the Zemzelett after Manipulating it.
Death Force - Makes one of your party immune to death - 3MP
Adamantaimai (beaches near Wutai)
Goblin Punch - Non-elemental attack on one enemy - 0MP
Goblin (Goblin Island). Goblin Island is a small island in the NorthEast corner of the map.
Magic Hammer - Drains 100MP from one opponent - 3MP
Razor Weed (Wutai, Da-Chao Statue)
Dragon Force - Raises Def and MDef stats of one ally - 19MP
Dark Dragon (Northern Cave)
Lv5 Death - Uses Death on all opponents with levels in multiples of 5 - 22MP
Parasite (Northern Cave)
Pandora's Box - Major non-elemental damage to one opponent - 110MP
Dragon Zombie (Northern Cave). If you want to learn this and actually use it, take the Right path in the Northern Cave, then get out of the Northern Cave. The only other place where you can encounter Dragon Zombies is on your way down the floating steps in the Northern Cave, on your way for the final encounter with Sephiroth. There is no way to get back up, so it is useless learning the Enemy Skill unless you intend to use it on Sephiroth.
Angel Whisper - Revives, restores all HP and status to one ally
Pollensalta (Northern Cave)
Shadow Flare - Extreme non-elemental damage to one opponent
The Ultimate Weapon uses this a final attack on the person who deals the killing blow. To get this, when you get to the final encounter with Ultimate Weapon (when he stops over Cosmo Canyon) give all the Enemy Skill materia you have to one person with a good lethal limit break (Cloud with Omnislash and Cid with Highwind or his Lv3 Limit Break where he attacks continuously are both great for this purpose). Carry out the Limit Break and the Ultimate Weapon should be defeated. (If it is not, repeat all over again). The Ultimate Weapon will then use Shadow Flare as a final attack, then will crash into the mountains.
Roulette - Death on one random ally or opponent
Death Dealer (Northern Cave). I haven't tried to get this one just yet, so I don't know of any problems you may encounter. I'll try and get it soon and post any notes.
????
I haven't managed to get this one yet. I think it's from an enemy in the Nilbelheim Mansion, but I haven't encountered any enemies who use this attack. As soon as I find something, I'll post it.