http://store.steampowered.com/app/200900/
Cave Story, a Metroidvania-type game resembling classic SNES titles, is probably one of the most well-recieved and popular indie games out there. It was also notable for being completely free; it has always been available as freeware for PC without as much as an advert. Now, it looks like an enhanced version's hit Steam. It's not free like the original Cave Story, but it's got extra content (most notably modes like a boss rush and new levels like the Wind Fortress) and promises future content updates.
Who's getting it? I think I might. It's a bit of a jump going from freeware to $10, so I hope that the extra content justifies the price.