Games For Windows - Live currently and soon to be on Steam and Impulse). It debuted on Xbox Live Arcade just last week and has yet to reach PSN -- though it's expected "in the coming weeks." Zombie is already working on the sequel, though.
Confirmed by our sister site Big Download, Zombie CEO Mark Long said his studio is aiming for a summer 2011 release for Blacklight: Tango Down 2 (working title). The sequel will feature larger maps than those included in the first game and implement mech-like vehicles into the gameplay.
Long also confirmed that there are currently no plans to offer DLC for the first Blacklight: Tango Down beyond patches to fix any persistent bugs.