It looks like a lot of indie games are 40-50% off already, so I'd expect some 66%-75% deep cuts by the end of the sale. From my wishlist:
Half Minute Hero: 40% ($6)
Din's Curse: 40% ($6)
Anna: 50% ($5)
Giana Sisters: 40% ($9)
Hotline Miami: 25% ($7.50)
Jet Set Radio: 50% ($5)
Avernum Bundle 4,5,6: 50% ($6)
Mark of the Ninja: 25% ($11.24)
No discounts currently on:
Retro City Rampage, Thomas Was Alone
Finally, Skyrim has a default 33% discount at the start of the sale, so I'm hoping it hits 50% for the first time.
EDIT: GMG confirms Skyrim and Dishonored at 50% this Friday