My own collection is but a shadow of its former self. There were many, many games I realized have been sitting around, either barely played or never finished. It's these games I knew I would never touch again, so I've either sold them, traded them in, or just gave them away.
The titles I keep, I keep because I know that I will unequivocally pick them up and play them from time to time. I won't list every game I currently have, but I will say that the number of titles below each represent about a third of my existing collection for each respective system. (So, for instance, I've got eight PS2 titles listed, which means I have approximately twenty-four PS2 titles total.) These just happen to be my absolute faves:
PSOne:
Beatmania (All of them. Eleven, I think?)
Brave Fencer Musashi
Bust A Move
Bust A Move 2: Dance Tengoku Mix
Chocobo Racing
Crash Bandicoot 2
Einhander
Guitar Freaks
Guitar Freaks 2nd Mix
Metal Gear Solid Integral
Point Blank 3
Pop'n Music (Again, all of them. I believe there were seven.)
Resident Evil 2
Suikoden
Suikoden 2
Umjammer Lammy
Vib Ribbon
PS2:
Ape Escape 2
Ape Escape 3
Capcom vs SNK 2
Contra Shattered Soldier
Gitaroo Man
Gradius V
Metal Gear Solid 2: Substance
Metal Gear Solid 3: Subsistence
Dreamcast:
Grandia 2
Jet Grind Radio
Samba de Amigo
Samba de Amigo ver. 2000
Soul Calibur
Virtua Tennis
GBA:
Castlevania: Aria of Sorrow
Double Dragon Advance
Kururin Paradise
Legend of Zelda: A Link To The Past
Legend of Zelda: The Minish Cap
Ninja Five-O
Rhythm Tengoku
Super Mario Advance 4: SMB3
Super Street Fighter 2 Turbo Revival
Wario Ware, Inc.
Wario Ware Twisted!
Gamecube:
Ikaruga
Mega Man X Collection
Soul Calibur 2
Viewtiful Joe
Viewtiful Joe 2
DS:
Bleach: The Blade of Fate
Castlevania: Dawn of Sorrow
Contra 4
Elite Beat Agents
Kirby Super Star Ultra
Nanostray
New Super Mario Bros.
Ouendan
Ouendan 2
Phoenix Wright: Ace Attorney
Phoenix Wright: Trials And Tribulations
Rhythm Tengoku Gold
Trauma Center: Under The Knife 2
Wii:
Boom Blox
Resident Evil 4 Wii Edition
Super Mario Galaxy
PSP:
DJ Portable MAX
DJ Portable MAX 2
Castlevania: The Dracula X Chronicles
Virtua Tennis 3
Parodius Portable
SNES/SFC:
Final Fantasy V (SFC)
Front Mission (SFC)
Seiken Densetsu 3 (SFC)
(This listing is an exception. These are the only three SNES/SFC titles I currently own -- and I keep them strictly for sentimental reasons. I don't even have an SNES to play them on anymore.)
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These two are exceptions as well, seeing as how I'm a late adopter, and these are actually all the games I currently own for each. (And like the Wii, I'm also not counting digital downloaded titles.)
PS3:
Call of Duty 4: Modern Warfare
Grand Theft Auto 4
LittleBigPlanet
Metal Gear Solid 4: Guns of The Patriots
Xbox360
BioShock
Blue Dragon
Dead Rising
Gears of War