Halo 2 online and campaign several months of online 6months 3-4 hrs a day. halo3 cod4 PS3 and 360 split time oblivion over 80 hours. ff7 beat 2x so close to 80 hrs on it other final fantasy's around 40 hrs to beat on avg. except 12 never played that or 11.

Off the top of my head, I'd say Civilization II. A short game of that takes about a day.

I've spent a good 100+ hours playing Final Fantasy, Chrono Trigger, Earthbound, Diablo II, Starcraft, Civilization II, GTA: San Andreas, Virtua Fighter 4: Evolution and Elder Scrolls IV: Oblivion. VF4E looks like it'll probably end up as my #1 most played game in my life, I punch at least ten hours into it every month.

Probably Super Mario Kart (SNES), Civilization 2 (PC) and GTA III (PS2)

Chrono Trigger, Link to the Past, Super Metroid( I play through them once every few months)
As for online, Quake 3 Arena, DOTA and CS combined must've claimed hundreds of hours of my life
In fact, in Quake 3 ,there's a particular map ( Q3DM17 for those who know) , which might have consumed 200 odd hours of my life

Civilization 2 PC.

Or maybe Gemfire SNES.

Probably Civ 2 though... hard to say...

The pure number of hours on it would be frightening.  I'll put it this way.  I've spend over 200 hours in front mission 3... and i haven't played that remotely as much.

NCAA football. I usually am still playin the old one when the new one comes out.

I mix in a ton of other games throughout the year, but I always end up playing a game of NCAA at some point.

COD4:MW. Over 14 days and counting

Civ2 PC, 2-6 hours per day for almost 3 years, is that enough?

oblivion pc.