1. Call of Duty MW1/2 online (about 40 days overall)
2. Final Fantasy XIII (4 completions and a platinum trophy, about 250 hours in total)
3. Pokemon Silver / Gold (so many AA batteries I cannot even count, so I'm guessing 150 hours)
4. Final Fantasy VII (2 completions and plenty of grinding, about 100 hours in total)
5. Grand Theft Auto: San Andreas (lots and lots of dicking around, I bought 3 copies of the PS2 version, the PC version and the XBL version, about 75 hours in total)