My top picks for the DS (aka the ones I've played the shit out of):
Meteos (it's like crack, in puzzle form)
Castlevania: DoS
Trauma Center
Phoenix Wright
Sonic Rush
Tony Hawk DS (it's not all that hard, but it's damn fun to play)
Mario Kart DS
I'm also pleasently surprised with "Trace Memory" thus far, but that's cause I'm a sucker for old school "point and click" adventure games. Too soon to tell if it will hold up in the long run though.