1. Gorf, Advanced Dungeons&Dragons, Baseball, and Tron: Deadly Discs
Included for nostalgic reasons, these are some of my favourite games from the first consoles we owned when I was very young. Gorf on the Commodore VIC-20, and then Advanced Dungeons & Dragons and Baseball (Yer out!) on Intellivision. My father and I played baseball until our hands hurt (not hard on the awkward controllers). I once (and only once) got 1,000,000 points on Tron: Deadly Discs and got to see the Guardians. (Just outside this list: Astrosmash).
2. Super Mario Bros. (I and III), Metroid, and Legend of Zelda
My cousins are part Japanese and had Nintendo at home two years before it came out in North America -- when it finally arrived, I had to get one specifically to play Super Mario Bros. Later, I went to see the crappy movie The Wizard just for the advance footage of Super Mario 3 (worth it) and I spent $80 of my tips from working as a busboy to get it as soon as it was released (worth it). And no, I don't need warp zones to finish either of them. Absent from this list: Super Mario 2. Metroid and Zelda also consumed many hours of my youth.
I pretty much got a Game Boy just for this game, having become hooked on it in the arcade. Easily one of the greatest games made.
4. Wing Commander (I, III, and Prophecy)
I don't usually like flight sims, but space ones I do. We played this game a lot in high school. So much, in fact, that we once left Wing Commander running on a computer in one of the classrooms, but managed to convince the teacher that it was a screen saver. It only got better with WCIII. Mark Hamill as Blair? Awesome.
5. Mortal Kombat
My buddy and I could finish this on one quarter when we were undergrads (yep, games used to cost 25c). Of course, we spent a lot more getting to that point. FINISH HIM! (Over, down, over, high punch).
6. Doom (I and II)
Not so scary now, but back then playing with the lights out and the sound up was a challenge.
This game is still popular and there is even a professional league dedicated to it.
8. Perfect Dark
This game was great for playing with my brother on his Nintendo 64. For starters, you could be on the same team and fight simulated agents. Is anything cooler than a laptop gun?
9. Warcraft III
This realtime strategy had amazing cut scenes and extraordinary gameplay along with an exceptional story line.
One of the best selling games ever, and for good reason.
Ok, your lists?