Monster Hunter Tri on the Wii. I put over 300 hours into that game alone and I played for about 14 hours straight.

World of Warcraft >9000 hrs (over a year play time)

For consoles/handheld it's  probably Fire Emblem Awakening. I've got 159 hours in that game so far.

In my younger days when I was in school, I hardly turned off the games I played which are mainly rpgs so I would clock in close to a thousand hours.

Yeah, admittedly, that's how I have 2707 played days on a character.   hehe

lol, that pun wasn't intended ^^

Yeah, but the opportunity was ripe for the taking :D

World of Warcraft - +/- 150 days
League of Legends - 54,3 days
Black Ops 1 - +/- 25 days 

then Age of Empires 2 and 3 and runescape also a lot

oh and I forgot tribalwars, easily tops my WoW playtime