Super Smash Bros. Brawl easily. Over 400 hours of play time (close to 600 hours of power time)

Fire Emblem Radiant Dawn by far in my case, followed by Guitar Hero III.

SSBB and who knows what followed by Twilight Princess at 100 hours (2 play throughs, lots of fishing, lots of messing around).

Mario Kart Wii still

New Super Mario Brothers Wii for sure.

Girlfriend and I first beat the entire game. Then we played through again and got every single coin.

Then we started over and played through the entire game until we got every single coin and had never had a single game over.

Now I need a sequel so we can finally stop playing it lol.

Metroid Prime Trilogy, Monster Hunter Tri, Metroid Prime 3, Valhalla Knights: Eldar Saga, Twilight Princess, Okami, Dawn of the New World, Super Mario Galaxy, Super Mario Galaxy 2, Super Smash Bros. Brawl, in that order. All of them are over 100hrs with the exception of the last four. Those are strictly Wii games. I have some Virtual Console games that clock higher than some of those. 

I'd have to check, but probably Mario Kart Wii.  Monster Hunter Tri will probably pass it eventually, but I'm taking a break on it for now.  I thought Smash Brawl would be a contender, but it's not even close and at this point I have little desire to go back.  If I ever want to play a Wii fighter, it'll probably be Tatsunoko Vs. Capcom for the foreseeable future.

Twilight Princess, Radiant Dawn and Okami are all getting up there though, after multiple playthroughs for each.  Also, I expect Metroid Prime Trilogy will get pretty high after I 100% all 3 games.  Also, Shiren the Wanderer will probably get up there when I finally pull it off the pile'o shame and delve into it.  I sunk nearly 100 hours into the DS game iirc.

easily cod mwr

The Legend Of Zelda: Twilight Princess played through the whole game like 4 times already

Brawl, around 800 hours with friends.