The actual list is way too huge to have in a single post here, but there'll be cheap game bundles, including 48 Genesis games for Steam for five bucks, loads of Magicka / Saints Row 3 / DLC packs, Lego / Normal Batman game packs, among other things. Some items are cheaper on certain dates, so make sure you visit on the right date to take advantage of the price!
(Game purchases are not region locked, but some folks are able to buy stuff even if they're not in the US, by using a fake address. YMMV. Very few keys are region locked.)
There's a list compiled and ordered by date created by Awkward1099 over at
Cheapassgamer. Props to him for taking the time to fill this out.