In case you were still on the fence about pre-ordering BioShock Infinite on Steam, the offered rewards will probably push you over the edge. Just like with Resident Evil 6, the more people who pre-purchase BioShock Infinite will mean that more freebies are unlocked, with the first tier, a free copy of BioShock, already at 91% out of 100.

As for the second tier, that has you unlocking exclusive Team Fortress 2 items for BioShock Infinite, which you can read about right here:

• Vox Diabolus: With this Vox Populi anarchist mask, you can terrify your enemies into thinking you're the Devil Himself, or worse, a protestor. Either way, they're probably going to avoid you at the entrance to the supermarket when you try to get them to sign something.
• The Pounding Father: Heavy cannot tell lie. Heavy is first President of United States. Of crushing little baby men.
• Blind Justice: Want to command respect from people standing at an indeterminate distance from your immediate right? Bolt on a platinum Pinkerton badge and experience the thrill for yourself!
• The Person in the Iron Mask: Turkey? Chicken? Game hens? Your head? This cast iron poultry furnace will smoke anything placed inside it.
• The Doe-Boy: Protect the important thoughts in your head -- ones like "liberty" and "freedom" and "democracy" -- with good, honest, hat-shaped American steel. This helmet won't run (until heated to 2500°F)!
• The Sydney Straw Boat: Throw this hat on the ground to express rage, or in the air to express joy! Take a hat-based trip through time to learn how your great grandparents displayed emotions in the days before emoticons!
• The Steel Songbird: It gets pretty quiet in that sniper's nest. Why not treat yourself to the haunting rhythmic symphony of bolts being constantly pooped by this mute, easily terrified incontinent bird?

The final tier, and easily the best, is a free copy of XCOM: Enemy Unknown. Based on the way pre-orders are already going for Infinite, expect this to be unlocked shortly.