Sonic Generations on Xbox Live and PlayStation Network. You can charge through a new(ish) Green Hill Zone with original (chubby) Sonic, and can sample the stereoscopic 3D mode while you're at it. Based on what we played, it doesn't appear as though the flipside of that level could be played with modern (skinny) Sonic. Luckily, we have 20 days to see if it's buried in there as an easter egg.
Sega released a free iOS App as well, though it's only found its way to the Japanese App Store thus far -- we've checked with Sega to make sure it's coming here as well. According to Andriasang, it'll only be available for the next six months. The app is composed of the first stage of Sonic the Hedgehog 4 Episode 1, a minigame named "Sonic the Sketchhog," a news feed, and an area for "weekly wallpaper downloads."
Sales are also kicking off on a variety of Sonic titles for XBLA/PSN, which run from today through July 28. And yes, this Thanksgiving, Sonic -- in his skinnier form -- will once again appear in the Macy's parade, taunting our turkey-swelled bellies with his simultaneously svelte and inflated figure.