Yeah, the One Piece Grand games are a lot of fun, if you can find them. eBay or a local indy games shop is your best bet.
Naruto Ultimate Ninja stuff is great too...#2 just came out, so the first one is in the bargain bin now (£12 at Asda). I'd still recommend the new one though....from Woolies or whatever.
The DBZ Budokai games are cool...I think Tenkaichi 3 is due out in a few months, but BT2 is great.
FMA DS is really quite tripe, and lasts as long as a KFC "large" fries.
Jump Ultimate Stars is fantastic by the way...only in Japanese, but you don't really need to read anything. Loads of characters from most SJ series...Naruto, Bleach, Death Note, HXH, blah blah blah.