That falls down to Everquest classic, I don't remember anymore but I logged hundreds of days (if not over a full year) played over like 4-6 years, and have quite a bit on WoW too.
Probably CS. I think I started a bit after/during beta (been a lot of years now), up through a year or so ago. Had some 3-6 month off periods, but played it pretty solid for like....6+ years
In no particular order: Microprose Formula 1 Grand Prix The Settlers Rockstar Ate My Hamster Civilization 4
Soldierfront: sfront.ijji.com, Not Very Well Known But ITs A Basic FPS That Isnt Trying To Be Crazy With Ideas. I've Been Playing Since The '07 Closed Beta *(Its F2P)*. And Just Came Back From A Years Break. I Tried To Play WoW But IT Just Bored To Deathhhh. Repetition Is Something I Hate. OH And Also Mw2/Black Ops (Me And A Few Friends Had A weekend Free So We Played Mw2 72 Hours Straight, Yer... Not Such A good Idea With Work Monday Morning.)
Long time ago when Final Fantasy VII came out I spent atleast 300hours on that bad boy. And still didn't finish everything. Good old times.