Any decent free games?

Free? Metro 2033 :P

There are maaaaaaaaaaaaany good free games, like TF2 and Dota 2 :)

I Wanna Be The Boshy

If you enjoyed Cave Story I would recommend eversion which also has a freeware version. It seems to be a very simple platform game at first but you'll soon see the twist.

On Steam you may want to check out Peggle Extreme. Again while it may not seem like anything special to begin with, you can easily wile away a quite few hours without even realising.

Don't know if this is too late and you already know but apparently Game do steam wallet cards now :) There was also a special deal that gave you extra if you traded something in towards it but I don't know if that is still going.

Edited with link Random news post

There is Steam Wallet in the UK, you can buy it from Game

Cave Story