Psycho Penguin said:
There's a ton of games anyone else will mention (Super Metroid, Mario 3, Mario Land, Pokemon, Goldeneye, Final Fantasy series) so here's a few that are pretty obscure.
Yo! Noid (NES) - A simple but fun platformer. I really enjoyed it growing up. Even if the pizza eating contests suck.
Adventure Island series (NES) - A very hard series of platformers. Playing the original is akin to trying to raise your blood pressure, but it's a lot of fun.
Dragon Warrior (NES) - This is one of the simplest, yet most addictive, RPGs I have ever played. It's a blast just to go around leveling up for hours on end. The "one guy vs. the world" mentality is awesome. Whenever I get sick of huge epic RPGs, I go back to this one.
Sonic Blastman 2 (SNES) - It's a beat em up, and doesn't do anything particuarly innovative, but I still play it nevertheless. It does everything well.
Raiden Trad (SNES) - I guess the fact it's one of the few shooters I can actually beat helps, but the soundtrack is pretty amazing.
TMNT II: Arcade Game (NES) - It doesn't even matter that it's not as fun as the Arcade version, because I still really enjoy it.
Legend of Legaia (PSX) - One of my all time favorite video games. The battle system has rarely been outdone in a RPG.
One (PSX) - Kind of like what Contra on PSX should have been.
Aww, reading that these are obscure has made me feel even older than the Guitar Hero: Metallica thread. ;D
In their own times pretty much every one of those titles was easily well known to me and my friends.
I usually fire up the emulators for a game of...
Punch-Out!! (any of them. Arcade, NES, SNES)
Bionic Commando (not so much since the remake hit)
Final Fight (I really liked the Gameboy SP remake, MORE than arcade amounts of enemies!? yes!)
Golden Axe (MAME for arcade)
Indiana Jones (on Atari 2600 because WTF it was a crazy game for it's time and seems crazier in retrospect!)
Fatal Fury 1 (pretty easy to play on a KB, I always lose my decent USB gamepads and it's hard to play fighters without one.)
Street Fighter (any of them but usually Super as Super Turbo is too mean and the gamepad issue again...)
Revenge of Shinobi (Genesis)
I used to play a ton of arcade games on MAME actually. Something very cathartic about getting some free shots in on those quarter munching jerks from my childhood. I was big into Neo Geo on my PSP too for a while.