Forgot to include The Orange box (360, PC), and soon to be Left 4 Dead (360, PC).

And I could throw in Half-Life 2 & HL2 Ep1, since I owned those prior to the release of The Orange Box.

Super Mario 64 - N64/VC
Zelda II: The Adventures of Link - NES/VC

Stand Alone:
Resident Evil 4 - GC/Wii

Compilation (Super Mario All-Stars):
Super Mario Bros. - NES/SNES
Super Mario Bros. 3 - SNES/GBA

Lemme see here...

Sonic the Hedgehog (Gen/Gen/GCN)*
Sonic the Hedgehog 2 (Gen/Gen/GCN)*
Sonic the Hedgehog 3 (Gen/GCN)
Sonic & Knuckles (Gen/GCN)
Sonic Spinball (Gen/GCN)
Dr. Robotnik's Mean Bean Machine (Gen/GCN)
Pokemon Red/FireRed (GB/GBA)
Super Mario World (GBA/VC)
Super Mario Bros. 3 (GBA/VC)
Mario Kart 64 (N64/VC)
Star Fox 64 (N64/VC)
Resident Evil 4 (GCN/Wii)

*Original Games, Sonic Classics, and Sonic Mega Collection

I only I bought twice while still being able to play the older one was Resident Evil 4. I bought the Wii version even though I still have the GameCube game in perfect condition.

I also bought Resident Evil: Code Veronica twice but I had sold my Dreamcast so I couldn't play the original anymore.

Also, most of my 21 VC games are games I owned at some point but traded or sold.

RE4 (GCN/WII)
Zelda OOT (N64/GCN)

-Assassins Creed
-Final Fantasy VII/VIII/IX(Its a good game people) Not that I sold those three titles but their in my room at my parents house overseas.....along with the rest of my 150 something game collection. *Eyes twinkle*
-Chrono Cross
-Resident Evil 2

Zelda 2 VC/Original

Secret of Mana VC/Original

SMB3 VC/Original

Paper Mario: TTYD

lost it so i bought it again, its so awesome

I accidentally bought 2 copies of Metroid II: The Return of Samus for Game Boy because I forgot I already had it. The rest were intentional. I'm also not counting the tons of replacement games. My mom gave away most of our NES games when we got a SNES, and I had to buy them again later.