I recently bought Paper Mario, it's very fun.
It doesn't have a lot of replay value, but it will keep you busy for a while.
If you want to max it out, once you beat the game, there are trading cards and recipies to collect.
There are also arcade games that give you tokens. With enough tokens you can get items that increase your HP and Atk.
I've been renting some games too, I got NFS: Carbon and I'm hooked.
I had to change the controls to use the nunchuck too. It took some getting used to, but it's very fun.
I'm going to rent Excite truck too, but I've been looking for a racing game and I think NFS fit the bill.