DS: Final Fantasy 4, now few hours into Fire Emblem but will be lots.
Wii: Mario Kart Wii, Zelda TP, Fire Emblem RD, Wii Sports (with friends)

Wii

Mario Kart Wii - 1-2hr every couple days, so I've probably played about 150 hours
Mario Party 8 - again 1-2hr every couple days until MKWii was released so probably 300 hours
Fire Emblem: Radiant Dawn - 4 play throughs, each about 40 hours recorded, so probably 250 hours total
Big Brain Academy: Wii Degree - no real clue, but I played it with my wife a lot, so probably 100 hours

DS

Advance Wars: Dual Strike - 40 hours
Advance Wars: Days of Ruin - 20 hours
Professor Layton - 12 hours

If we counted GBA games, I would have a few with a lot more hours, like both Fire Emblems, and both Advance Wars.

Wii

Mario Kart Wii
Sonic & the Secret Rings
Super Mario Galaxy

DS

Yu-Gi-Oh! WC2008
Pokemon Diamond
Castlevania Order of Ecclesia