A whole mess of Sonic the Hedgehog content has rolled onto Steam today. First up, Sonic CD, which has already debuted on PSN, Xbox Live and mobile platforms, has now made its way to Valve's ubiquitous service. Joining it is Sonic the Hedgehog 4: Episode 1 and the Sonic Generations "Casino Nights" DLC that was previously scheduled to arrive on December 26.

Though it's not a Sonic game, Sega's free-to-play Spiral Knights is getting some Sonic-themed content as well. Players can pick up a Metal Sonic costume or a Tails accessory (i.e. a pair of fox tails). Spiral Knights is free, but these items are not. The Metal Sonic costume comes free with Steam copies of Sonic CD, while the Tails accessory will require an in-game energy purchase. Both items are available until February 1.

Head over to Sega's blog to check out images of the new goodies.