Well I'd go with the Ratchet & Clank series. Challenging, but usually not too frustrating, well made and fun to play! Really a good series of platformers.
As for non-3D, anyone that never played Earthworm Jim 1 and 2 on SNES/Megadrive(Genesis) missed great games in the platformer genre
they are favorites of mine.
There are many other releases that came out on different platforms after that, but didn't play them so I don't know if they are any good.