The Pushmo series. Puzzle games involving the manipulation of 3D structures. Very original and challenging.
Also, on the 3DS if you are into Pokémon, there's the VC GBC games (Red/Blue/Yellow; Gold, Silver, Crystal). Not only it's the only place they can be legally purchased, but they are compatible with Pokémon Bank, making them the only way to transfer 8bit Pokémon to modern games.