im sorry but avoid Sonic Unleashed like HIV, that game was a let down. the day levels are fine, but once you get to night, the controls are a hot mess and it plays like a poor man's God of War. It wouldnt be so bad if there wasnt so many of those levels and they were so long

Epic Mickey, de Blob, Sonic Colours, Klonoa...

probably the best IMO.

3D:

de Blob, de Blob 2, Epic Mickey, Sonic and The Secret Rings (an underappreciated game. it had some controls issues, but aside from those it's the best sonic since the last generation), Sonic Colours (i didn't liked it that much but everyone seems to think it's the best sonic in years, so you should give it a try), Mushroom Men (another underappreciated game. i think it's kinda hard to find now, but it's a fine platforming experience much in the vein of  platforms from the 1990s)

Jett Rocket on WiiWare is also pretty good.

just stay away from sonic unleashed and sonic and the black knight, they are downright horrible!

2D:

Klonoa, A Boy and is Blob, Lost in Shadows (known as A Shadow's Tale in europe), Ivi the Kiwi?

you should also try the 2 LostWinds and NyxQuest on WiiWare

i know you asked for non-nintendo platformers but if you haven't  played it yet you should also consider Donkey Kong: Jungle Beat from the New Play Control line.

3D only Sonic Colors and thats pretty much it.

Some good 2D ones even some great ones on WiiWare.

If you are looking for 3D platformers, you'll not find anything better than the SMG games anywhere.

But I would highly recommend the Wii edition of Donkey Kong: Jungle Beat. Very disappointing that nobody mentioned it. It's made by Nintendo (the same internal studio that developed the Galaxy games), and not Retro. It's shorter than Returns, but top quality throughout. One of the best 2D platformers of the last 10 years. 

Also, look into Klonoa Wii. 

But isnt that a music game? If its another Donkey Kong platformer, than i dont need to hear ANY other suggestions. I would buy it first thing tomorrow.

No, it's a 2D platformer developed for the GameCube by Nintendo. It was critically acclaimed, but not too many bought the game because you had to control it with the bongo drums which were developed for the Donkey Konga music game (made by Namco). 

The Wii edition lets you control the game with the wiimote and the nunchuk. 

Its an absolutely beautiful game with very imaginative level designs. It's NOT as long, varied or hard as DKCR, but its amazing anyway. In fact, when I first played Returns I thought it had more in common with Jungle Beat than the SNES games. 

And it has underwater levels by the way. 

I will never converse with you again.

omg this!!

I adored Jungle Beat! - Though it's not your typical platformer, it's SO wonderful and fun to play :D

They are overrated IMO because of the simple fact there is little to no platofrming in SMG ( i havent played SMG2 till the end, so I cant say) you spend most of the time spinning and running with power ups on enemies. Its not an actual platformer IMO. SMG2 is way better thou, since it has some actual platforming. And dont get me started on underwater controls...just utter horrible and unplayable.