Green Man Gaming has Sonic Generations for preorder for $25.45 (15% off the standard PC price of $30). http://www.greenmangaming.com/games/...c-generations/ However, they've also just launched an autumn 20% off sale - which stacks with the 15% preorder discount. If you use the coupon code AUTUM-NSALE-20PEC, you can get the extra 20% off for a total price of $20.36.
You have NO excuse not to buy at that price.