Psssh the metal slug series trumps all

Prince of Persia: Sands of Time. Just pure awesome in every way.

Ionami:
Conker's Bad Fur Day (the N64 version)

I'll drink to that brother.

Banjo-tooie!

Voodoo Vince, Blinx, Crash Bandicoot...and Super Mario Bros on Gameboy Colour. Speaking of Gameboy Colour, there was a game with Bugs Bunny in it, Crazy Castle or something of the like. That was fun.

super mario world. all the fun of the older games, with better graphics and a explorible world map. Mario 3 was good too, but I like the variety in World better, and the cape is far superior to the tail. though I do miss the P wing.

The only other platformer I really love is this ancient computer game made by epic megagames called jill of the jungle. pretty obscure, your just this little blob of pixles that look vaguely like a blond chick, jumping through the woods throwing knives at giant bugs and stuff. It was one of the first platformers I played though so it has a special place in my heart.

Rick Dangerous.

Super Mario World

Alex Kidd in Miracle World... for those younger gamers: http://br.youtube.com/watch?v=3OxK_2EP2K4

Kirby's Dreamland for Gameboy(c) is good because, as you can fly, it is unlikely you will fall to your death which is my worst enemy in platform games (failing the same jump hundreds of times is not fun) but I can't really say it's the best as I havn't played a lot of other platform games.

smon:
I agree with Stammer, definately Sonic 3

I've always been a Sonic 2 kinda guy.

Never really played Sonic 3 in my youth, but i can't stop playing Sonic 2. I still play it a few times a year!

"Samus series"? Samus series!?
It's called the Metroid series! I take offense! How'd you like me to go around talking about the Master Chief series?
*cough* sorry about that.

Anyway, my favourite platformer is Super Metroid. Fucking awesome, that game.
If you wanna specify 3D platformers, then I'd have to go with Super Mario Galaxy, in no small part because of the (ironically) 2D platforming segments

Honourable mention also goes to the Kirby series in general.

Jumpman:

The only other platformer I really love is this ancient computer game made by epic megagames called jill of the jungle. pretty obscure, your just this little blob of pixles that look vaguely like a blond chick, jumping through the woods throwing knives at giant bugs and stuff. It was one of the first platformers I played though so it has a special place in my heart.

I thought I was the only one who knew Jill of the Jungle! I loved that game!

Donkey Kong Land 2 on the Gameboy. First game I ever owned. It was beautiful.

Crash Bandicoot 2/3

You could kill things with a belly flop, what more do you need? The original citrus Bazooka? We've got that too.

The first platform game i played with utter glee was Donkey Kong Country, so that's always gonna have a special place with me.

Also:
- Megaman X
- Bubsy the Bobcat in Claws Encounters of the Furred Kind
- Super Mario World (and Yoshis Island)

Crash Bandicoot and Spyro the Dragon were the first platformers I ever played, but Jak and Daxter would definitely be on the list as well. Also Klonoa, if you can really call it a platformer

Legacy of Kain: Defiance, By far the best one.

tindol_1:
seriously, platform games, back in the day mind you, we're the most fun a six *ahem* year old could have with his game console.

2D(True Platform) : Super Mario Land. 99a indeed.
3D(Action Adventure) : Prince of Persia: Sands of Time.

The original Sonic the Hedgehog. The only game I still play on my Mega Drive. Apart from Fifa 95 of course. I love Fifa 95.

Oddworld. Need I say more?

Trivun:
Crash Bandicoot and Spyro the Dragon were the first platformers I ever played, but Jak and Daxter would definitely be on the list as well. Also Klonoa, if you can really call it a platformer

Every single Klonoa game, with the exception of Klonoa Beach Volleyball and some obscure Japanese RPG that never crossed the shores, has been a brilliant platformer. Kinda tricky to track down, but well worth it.

Super Mario Bros. 3.

Ok, for nostalgy reasons mostly, it was the game that made me a gamer. It's good, but Super Mario 64 was a lot better.

Jazz Jackrabbit! Fast, fun, good cutscenes, awesome main character.

I'm gonna have to go with the following:

Megaman X: Zero 1-4 (though the quality went up from 1 to 2 and then seemed to go down after that, plus I never had a chance to play any of the other games in the series really)

Megaman ZX and ZX Advent (not the best but very fun)

Metroid Fusion (never really had a chance to play any of the others)

Prince of Persia Sands of Time (The Two Thrones wasn't bad either, but definitely not as good)

Ratchet and Clank (whole series. Oh the weapons are fun)

Jak and Daxter/Jak II and III (except for, of course, that racing game)

N+, I love the co-op and level designer.

No love for Rayman?

Commander Keen 4-6!

sonic

No one? Okay, I'll say it. Castlevania: Symphony of the Night

Puppeteer Putin:
Oddworld. Need I say more?

Those games were great. There's only one thing better than mind controlling enemies, and that's being able to blow them up when you're done with them. And it had the whole moral choice thing already, which was pretty cool.

Crash Bandicoot 2 and 3 were great too, but 1 was so frustrating. And Spyro, that's was good too.

gigastrike:
Banjo-tooie!

I see I've already voted. Oh, well. My answer remains the same.

Oddworld on PC, and most recently the browser games Fancy Pants 2 and Super Mario 63.