God, where to begin? League of Evil, Mos Speedrun, and Super Crate Box are my favorites. (League of Evil 2 is coming in a few days actually...) Bean's Quest, Terra Noctis, and Paper Monsters are amazing as well. Those 6 are widely considered some of the best, so you can't go wrong.
Any of those plus Robot Wants Kitty, maybe Pix'n Love Rush HD, and for sure Crazy Hedgy if you're looking for a great 3D one. It uses tilt controls, but from what i've seen (note i've only played on an itouch) the controls are some of the best out there.
Another vote for Mos, LOE, and RWK, and three that haven't been mentioned yet: Shantae, NyxQuest and Mystery of the Japanese Werewolf. Edit: Actually scratch RWK unless you don't mind playing in 2X mode. Knew there was some reason I didn't have that installed...
It's not as good as most of the others listed, but still decent. Also be sure to buy League of Evil 2---it's releasing on the 15th for a buck and it's gonna be awesome.
Gotta second Bean's Quest. The controls and it being Universal make it a GREAT iPad game. Niko is pretty good too...
another world perfect cell soosiz HD Storm in a tea cup Infinight Frogatto Sonic CD Aquaria 1 bit ninja meganoid stardash kami retro plus all the previous suggestions.
Pizza Boy! Pizza Boy is my favorite platformer for iOS! Even though it's not Universal, I play it on my iPad all the time. TouchArcade reviewed it here.
I love platformers, but for most of them I enjoy them on the iPod more than the iPad. League of Evil, MOS Speed Run, and a whole lot of them mentioned above. The ones that I really enjoy on iPad are essentially the ones which have the following qualities: 1. Pleasing looks. 2. Don't make me take my hand off to press buttons all over. With these considerations, my favourites on the iPad have been Frogatto, Terra Noctis, Beans Quest (not trying to achieve the par jumps), Paper Monsters, Cordy, Babylonian Twins. Nyx Quest actually doesn't satisfy the 2nd criteria, but it's so darn good looking and zen-like that I finished it on iPad. Crazy Hedgy and Gears are two rolling sort of platformers which are really a million times more fun on the iPad. A special mention to Gears, which I think is the most under-rated and high quality CM game.
It was mentioned in the first reply I bought it a couple weeks back but still haven't gotten around to playing it, looking forward to it though given the many positive impressions I've read.
I'd say Lostwinds (though it looks very ugly on iPad because it renders in really low res for some reason), NyxQuest HD, Sonic 4 HD (if using iPad 2, it's slow on iPad 1), Giana Sisters, Mega Man X (mediocre iPhone port of amazing SNES game, but mediocre port is better than no port!), Pix'n Rush, Sonic CD (my favourite game!) and of course, Awesome Land!
Cordy 2..A very high quality action platformer,it can even match-up to the console titles...For me its the best on iOS... A masterpiece..
Incredible Jack didn't really do anything for me... It reminded me of another platformer - Supercow, which also did nothing to impress. =o/ But gotta go with Alister - Cordy 2. I'm also sticking with Bean's Quest - these are two platformers I LOVED on my iPad. The controls were incredibly comfortable, graphics were outstanding, and gameplay is top-notch/'console-quality'.