fallout3 with all expos
Dawn of War with all expos
metal gear solid 4
super metroid
sega genesis collection

I would bring a backwards compatible ps3. And:

MGS Essential Collection (ha! It counts!)
MGS4
Burnout Paradise
FFXIII
a Wii:
Super Smash Bros Brawl.

I wouldn't want to bring too many games I already played, what's the point?

Well, on a desert island, you're going to want endless replayability.

Assuming you don't have internet access, that means we're not talking about online multiplayer. Honestly, I think a game like Tetris DS would be on the list, because that is fun forever.

Final Fantasy XIII
Guitar Hero 3
Rock Band 2
Demon's Souls
DJ Hero

(with all expansions).

Touhou: IN,
Megaman X4,
Smash Bros. Brawl,
Super Mario World, and
Wii Music

for me

Now that I'm seeing other's answers it's making me rethink mine.

Burnout Paradise would be great.

And a RTS. Never really played any much because I never had the time...

Hmmm, really hard to make a choice, but I think:

-Age of Empires 2 (YEAHHHHHH)
-GTA San Andreas (PS2)
-I'll have to say Fallout 3, I'll replay the whole game if I have to, just for the sake of my sanity.

Need to think about 2 more games, no internet = Really hard to tell
But if somehow I had internet there.

-Counter Strike: Source
-COD4 (or RTCW)

Oblivion GOTY Edition
Fallout 3 GOTY Edition
Dragon Age: Origins including all DLC
Rock Band 2 including every created music track.(Hey, it's still 1 game!)
Age of Empires 2 Gold Edition(I could create scenarios endlessly)

ok..........
Chrono Trigger (ds)
New Super Mario Bros Wii (wii) .... endless replay value even in single player
Chrono Trigger (snes)
Mario Kart Wii (wii) ... same as nsmbwii
Chrono Trigger (psx)

...

I think I'm forggeting Chrono Tigger