Microsoft is offering one-day discounts on Sonic the Hedgehog 1, 2, and 3, (now 200 MS Points each), Sonic & Knuckles (120 MSP), Sonic Adventure (400 MSP) and Sonic the Hedgehog 4 (800 MSP). The Sonic car Avatar prop is on sale for 120 MSP.
Also, The Notebook is discounted today to 380 MSP. We don't think that's part of the theme, but if you're buying all those Sonic games, you should probably go ahead and buy The Notebook to try and spot any Sonic the Hedgehog references in it. Just to be sure.