All Pain, No (Materia) Gain - Obtain all character's ultimate weapons

Don't Like Suits - Encounter (and defeat) the Turks in all optional locations that you can find them

ZolOMG - Defeat the Midgar Zolom BEFORE entering the Mythril Cave for the first time

Sharpshooter - Score 100 successive points in the Gold Saucer basketball game

Digital Champion - Win the 'rock-paper-scissors'-style fighting game in the Wonder
Square

Bless You - Collect 99 Tissues

Skillful - Obtain all Enemy Skills

Memory Jogger - Get the full story of the Gold Chocobo from the Chocobo Sage

Armageddon Fist - Yeah! all of Tifa's 8 reels

(or alternatively)

Armageddon Fist - Win the Scarlet vs. Tifa mini game on the Sister Ray without getting hit

Makings of a Hero - During the Kalm flashback, Cloud must not die in any battle (this is kind of silly, because it is pure chance if you survive or not)


All I can think of for now. It's fun coming up with the names of these! =]