Birden - Insanely difficult browser based platformer

If you thought Meat Boy was difficult or even vvvvvv wait till you try Birden from Bitendo Software. A game in which you must avoid all the spikes, traps and enemies to reach the exit, but I guarantee you will not last long as you will die over and over again in frustration. As a bird you can flap about to avoid these deadly devices but wrong one flap and it's instant death (and level restart). Not just that but the developer has decided to make the character like an elastic band, which ends up with you bouncing and sliding all over the place, thus you have been warned!

Subdog Underwater Adventure - The pixeled submarine adventure that's just a little too difficult, but still fun!

Subdog Underwater Adventure from the newly founded indie game developer Dark pixel & Osky Studios is a rather difficult game with pixelated graphics and fun game play for android devices with flash and PC coming soon. Your little doggy has launched himself into the sea in search for his bone stolen by a marine creature. But be warned as this isn't an easy game, as not only do you have the sharp edges to contend with, but many deadly enemies and traps. If you touch one, your snorkel will not save you. This is a free game, with plenty of things to do, but the only down side are the ads, but don't let that put you off, this is a neat game!

Surface - Free Arcade Platformer with hardcore difficulty

Game Type : Arcade Platformer
Developer : PixolPalette

Game Info Quote : Surface is an Arcade platformer, where you traverse up each stage as fast as you can while avoiding hazards and enemies that will attempt to stop you. With 6 stages: 4 normal, 2 mini challanges, and 1 secret stage, there's plenty to do in Surface.
Release : Now (Free)
Systems : Any (Browser Based)

Sarif - Hardcore Platformer Puzzler

Another VVVVV style game is on the block, this is Sarif, in which difficult comes as the main pointer of the game. Be prepared to die over and over again, while struggling to deal with all the spikes and all the fun gravity puzzle solving goodness.

TowerClimb - Permadeath Platformer

TowerClimb is a game which the developer claims is a difficult and rewarding procedurally generated platformer. What that means is, when you die it's permanent and every time you restart you're a different person in a different Tower.