Worms: Reloaded on PC. Altogether, there are four packs to be had, including the Puzzle, Forts, Time Attack and Retro packs. Each pack includes new single-player missions, hats, gravestones, speech banks, landscape themes, and achievements. For a "limited time," each DLC pack costs $4.24 apiece, 15 percent off the usual price.
A note for Mac users: the DLC is only compatible with the PC version of Worms: Reloaded. Team17 tells Joystiq that work began on the DLC "quite a long time ago when the game was solely a PC title," and thus the packs are incompatible with the Mac version. Team17 currently has no plans to bring the DLC to the Mac version, but will "see what happens."
In addition to the new DLC, the full Worms: Reloaded game is part of the Steam Summer Camp Sale. It can currently be purchased for $10, half the normal price.