Any games like megaman or mario on steam?

mighty no. 9
A.R.E.S.: Extinction Agenda

Giana Sisters is a lot like Mario

SEGA Mega Drive Classics Pack

http://store.steampowered.com/sub/4839/
http://store.steampowered.com/sub/6016/
http://store.steampowered.com/sub/6486/
http://store.steampowered.com/sub/7095/
http://store.steampowered.com/sub/14445/

Oniken is pretty good too: http://store.steampowered.com/app/252010/

Also Life of Pixel: http://store.steampowered.com/app/327260/

If you're out luck try Cat Mario (web browser flash based game).

Gunman Clive and Shovel Knight are similar to Megaman and Bit Dungeon II is similar to the first Zelda.

http://store.steampowered.com/app/314710/ Says september, not december.

What about Braid?

There are plenty if you look for them

If you want a never ending, ever increasing in difficulty platformer, here is Cloudberry Kingdom.
Maybe some Broforce if you want a more run and gun fix.

Or you could search by tags on steam and look at some of the top sellers. Like the platformers tag which may be what you want. Plenty of great games to choose from.

cave story is a bit like metroid

A well underrated game:

8bitboy - http://store.steampowered.com/app/296910/

Not on steam, but here is something that should keep you busy for a while

Thanks guys, i appreciate the responds. :)

http://store.steampowered.com/app/237630

Found it as well. :)

20XX- http://store.steampowered.com/app/322110/
It's like Mega Man.

Shovel Knight
Eventhough it's a new game, it gives the feeling of an good old game.

Hopefully Alpha Ver. 0 soon.

I'm surprised no one said SUUUUPER MEAT BOY yet! It's painfully fun. Yes, you will feel pain, but it will feel good.

Explodemon

Not sure if this has been mentioned