In terms of games I always go back to and play over and over:
Battlefield Bad Company 2. I play this all the time on Ps3 and 360 both since opening day. I have at least 700 hours on it. By far my favorite game from last gen, and I would say Vietnam is also the best DLC ever made.
DooM 1 and 2. I play through these at least twice a year entirely and multiplayer whenever I can get someone into it. I play them on browser, SNES, PC, PS1, PS3. I love the N64 version too but it looks TERRIBLE on large HD TV's. That version needs a remake so bad...great games. DooM 1 is my favorite game ever made and has unmatched level design.
NBA Jam and NBA Jam on fire edition. I play these on Genesis and PS3 respectively. Never get old
I play through Super Metroid and Castlevania Symphony of the Night about once per year.
I play Quake 1 and Quake 3 multiplayer as much as I can. Mostly Quake 3. It is hard to find people who want to play 1 even though I would say it is the best multiplayer shooter ever made. Completely flawless 1v1. Tons of people still play 3 on Quakeworld.
Tetris.
All the NES Castlevanias
Final Fantasy 7
