Most of it isn’t surprising, games from early to mid 2011 are significantly reduced in price, Indie games are nearly free, hell, even some games that came out mere months ago are reduced to ridiculous prices. If you play games mainly on a PC, or even just do it part time, I highly suggest you pick up a couple of games.
Some of the better deals I’ve seen include:
Dead Space 2 for $5
Call of Duty Modern Warfare 2 for $15
Bulletstorm for $10
Need for Speed: Hot Pursuit for $10
GTA IV: Complete Edition (includes both DLCs) for $25
Now, I could just list all the deals but these are the ones that stood out most to me. I encourage you to check out the deals for yourself as not even most retailers could match these prices.
All the Autum Sale deals can be found on the store page of Steam or at http://store.steampowered.com/.