oh man, where do I start with my list
PS1
Metal Gear Solid - Cleared both endings (Otacon and Meryl), Unlocked Tuxedo Snake and Red Ninja, Recieved the Big Boss Rank (only hard thing is the time)
Resident Evil - Im sure you all know the unlocks for RE games, but I also cleared the game with only my pistol

(of course the Rocket Launcher came in to play at the end).
Resident Evil 3 - THE ORIGINAL MERCENARY MODE WILL NEVER BE TOPPED.
OPERATION MAD JACKAL FTW!!! (also cleared this game with only a pistol)
N64
Goldeneye 64 - That game is 25% of my life (the others being Mortal Kombat, Tomb Raider, and Soul Calibur) and probably the greatest FPS. If any of ever wanna play online, let me know.
PS2
Metal Gear Solid 2: Substance - Cleared All VR Training Missions, Snake Tales, Unlocked All Special Items (havent collected all the Tags though)
Evil Dead: A Fistful of Boomstick - Found all spells and hidden weapons
Resident Evil 4 - Not even gonna go down this list of unlocks (RE4's Handcannon is sick though)
GameCube
Crash Bandicoot: Wrath of Cortex - 106% (because of what it took to unlock everything, I'll probably never play another Crash game)
Soulcalibur 2 - Imo, this is the best Soul Calibur.
GBA
Crash Bandicoot 2: N-Tranced - on my 17th birthday, my parents got me a GBA SP and that was the first game I had. Stayed up all night and maxed it out.
Power Rangers: Wild Force - A repetitive, but cool game at the time. It takes 2 playthroughs to unlock every megazord.
Frogger's Adventures: Temple of the Frog - This game is simple, but requires strategy to grab all the coins and 1ups. If you dont believe me, start up an emulator.
Teenage Mutant Ninja Turtles - Collected all crystals and unlocked Shredder's Hidden Stage. This is one of my favorite Beat'Em Up games. Four different characters and completely different stages and bosses for each of them. Takes a lot to max out this one.
Dragon Ball Z: Legacy of Goku - Completed All Side Quests and found all secrets. This game is ridiculously difficult, but clearing it makes you feel heavily accomplished.
DS
Star Wars Episode III: Revenge of the Sith (DS) - First game I got for DS. Once again, attempted stayed up all night maxing it out, but I had to clear several times so it took maybe a week or so.
Resident Evil: Deadly Slience - This game was awesome, but the Auto-Aim made it a little bit easy, and there was no Infinite Magnum. I still never got to play Multiplayer (Didnt know many 19 - 20 year olds with DS's).
Castlevania: Portrait of Ruin - My favorite Castlevania game ever. Took me like a year (okay, maybe two) to max it out, but this game is worth it.
Castlevania: Order of Ecclesia - This one was kind of short and didnt really live up to Portrait of Ruin. Still, Maxed it out in a week.
Mario Party DS - Probably the only game I played with my brothers and sisters a lot(besides Goldeneye 64), until they stopped playing games with me because I always win.....sissies.
I'm a little bit tired from all that, I'll continue this list later...