If you haven't tried getting the all the Enemy Skills yet... you don't know what you're missing. I've found that this is one of the most powerful materias the game has to offer. It has everything from restoring life, to restoring magic, to absolutely slaughtering enemies.
Frog Song
Learn from: Touch Me's in Gongaga, or Toxic Frogs in the Temple of the Ancients.
Chocobuckle
Use Level 4 Suicide on a level 16 chocobo. They can be found around the Chocobo Farm.
Level 4 Suicide
Mus, around the Chocobo Farm, will use it.
Beta
Midgar Zolom in the swamps near the Chocobo Farm
Matra Magic
Enemies in Corel Prison (right before you encounter Dyne), and in Gongaga.
Golden Punch
There are Goblins on one of the islands in the Northwest corner of the map.
White Wind
Zemzellettes (I don't think that's the correct spelling) have it, near Junon on the barren type landscape.
Shadow Flare
Zombie Dragons in the Northern Crater (disc 3), and the Ruby and Emerald Weapons use this as well.
Magic Hammer
Can be learned from the Razor Weeds on the mountain of the 5 gods in Wutai.
Aqualung
Chimera uses it if you ride around in the desert by the Gold Saucer on the buggy.
Jenova Life uses it in the City of the Ancients after Sephiroth stabs Aeris.
Big Gaurd
Fight the Beach Plugs on the beach near Costa Del Sol.
Angel Whisper
Pollensalita has it in the Northern Crater. (disc 3)
Dragon Force
Manipulate a Dark Dragon in the Northern Crater. (disc 3)
Death Force
Adamantais have it on the beaches around the Wutai area.
Flame Thrower
Arc Dragons in the Mythril Cave (after crossing the swamp) will use it on you.
Laser
Dark Dragons in the Norther Crater (disc 3) have it.
Bad Breath
Molbor in Gaea's Cliff (after the snowboarding event).
Trine
The Materia Keeper (boss) in the Nibelheim mountains will use this on you.
Magic Breath
The Stilv on Gaea's cliff uses it.
????
Judge in the Shinra Mansion has it.
Level 5 Death
Parisites in the Northern Crater. (disc 3)
Death Sentence
Sneaky Step in the Cave of the Gi.
Death Roulette
You can get them from the Death Dealers in the Norther Crater. (disc 3)
