this website you're reading, Ronimo Games' Awesomenauts is now available on Steam. You can pick up Awesomenauts on Steam in three flavors: the standalone game for $9.99, the game with the soundtrack for $11.99, or in a three-pack for $19.98. The soundtrack is also available as a $2.99 download.
The Steam version is Windows PC-only right now, but it hopefully won't be a long hold-out. Ronimo Games has said the Mac version will launch "shortly afterwards" the PC version is available.