- A Dark Room http://blog.doublespeakgames.com/news/a-dark-room-goes-open-...
- Spelunky http://www.spelunkyworld.com/original.html
- MechCommander 2 (shared source, via Microsoft) http://www.neowin.net/news/microsoft-mechcommander-2-shared-...
- Asteroids (and many other Atari games) http://www.atarimuseum.com/videogames/consoles/7800/games/
- Cart Life http://www.spelunkyworld.com/original.html (perhaps not as commercially successful as the others...but won a huge indie game prize, and is a great work overall)
Spelunky was released as freeware so I'm not sure it counts.
Not as noteworthy as those in the list but hey, it's mine.
that said I'll add to the list DROD (one of the best puzzle series ever):
"Ryzom Core is the open-source project related to Ryzom Game. Written in C++, Ryzom Core contains the whole code (client, server, tools) used to make the commercial MMORPG Ryzom. Ryzom Core is a toolkit for the development of massively multiplayer online universes. It provides the base technologies and a set of development methodologies for the development of both client and server code."
Playing it, even with a walkthrough, is like watching a whole set of seasons of Babylon 5 or Battlestar Galactica.
So trying out UQM (open-source port) is a must.
It also has quite good two player fighting mode.
After reading this article, I compiled Duke Nukem 3D and played enough to find something that bothered me. Just pushed a fix for horizontal mouse-look/strafing (to Fabien's 'chocolate' repo):
It's like this weird connection to the original devs ... and my childhood.
Beware gnarly 6502 assembly language :-)