2D platformers seem to have experienced a revival in the last few years, especially on the Wii. (old news, I know, but I´m kinda slow to catch up on these things... or maybe I´m just slow in general)
New Super Mario Bros
Donkey Kong Country Returns
Kirbys Epic Yarn
Rayman Origins
Cave Story+ and Eversion are both games you can find on Steam and are excellent, or you can grab their original versions for free from their respective websites.
If you want to play something different, try NYAN-TECH. It's an Xbox Indie game where you need to press or hold buttons to activate the platforms akin to video game Twister. It doesn't have the length to rival Super Meat Boy, Sonic Generations, or others, but damn if the originality of its concept doesn't make it something truly special to play.
The Genesis version of Ghouls and Ghosts on VC is very good. I don't quite like Super as much, but it'(s a good game.
Also, Castlevania I, III and Rondo.
Posts
http://www.youtube.com/watch?v=by_yUyykZig
Shank
Mega Man 9 & 10
Braid
That's a good place to start.
Edit: Limbo the 2D platformer that is, not Limbo the drunken party stick game.
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Also, Castlevania I, III and Rondo.