I know this is somewhat preemptive, but I wanted to throw it out regardless since I just stumbled upon it:
Prototype Deal on Amazonl: Prototype + Prototype 2 + Radnet DLC for $9.99 starting Sunday, reportedly Steam keys.
Also, the deal is going to be even cheaper during some Gamespot show, supposedly starting tomorrow according to
this.
Some more info can be found
here starting at the bottom of the page, talking about all this goodness
Also,
Dark Souls Weekend on Steam, $26.79.
Death Rally Weekend on Steam, $3.49.
Another future deal on Amazon (that'll be updated when active)
$9.99:
S.T.A.L.K.E.R.: Shadow of Chernobyl
Metro 2033
Red Faction Guerrilla
Homefront
Red Faction Armageddon
Space Marine
Individual Steam keys, except for Stalker and Guerrilla, but it's possible that they will be Steam keys.