Because you can still play GC games on the Wii, I'll throw in Custom Robo (and to a lesser extent Custom Robo Arena for the DS).
Now of course, in Japan (not quite sure on the EU market) they released all the Custom Robo games and its made itsself a little series. Here the NA market, there's only two. Custom Robo Arena is... alright, though it wont exactly wow you like Custom Robo will. Its just a fun robo building fighter game that I think went very underappreciated because it was on the GC exclusively and because it didnt grab the attention as a console defining game.
EDIT:
well, my suggestion was already suggested (I dont like using the term here for it), but I'll keep it there so that the person that beat me can see at least two other people (at time of type) enjoy the game and know about it.
I'll add Izuna, legend of the unemployed ninja. Its got a sequel too (thought I havent played it). Sure, its not the deepest or best game, but for a JRPG its a pretty good portable game of its genre, and has some humor about itself thats pleasant to see.