There are 4 deals on Steam from Bethesda this weekend and you dont have to pre-order New Vegas to take advantage of the other three offers! There is also a great 50% off deal on Team Fortress 2(see edit below).
Fallout: New Vegas is US49.99 (comes with bonus in game caravan pack) pre-order http://store.steampowered.com/app/22380/ (Fishpond are advertising this for 79.97 for pre-order)
Fallout 3 GOTY only US24.99 http://store.steampowered.com/app/22370/
The Elder Scrolls IV:Oblivion GOTY Deluxe just US8.50 http://store.steampowered.com/app/900883/
The Elder Scrolls III:Morrowind GOTY just US5.00 http://store.steampowered.com/app/22320/
OR
pick up all 4 games for US88.48! http://store.steampowered.com/sale/bethesda_weekend
I'm not a big fan of Morrowind as it seems a bit dated to me but I would definitely recommend Fallout 3 and Oblivion at those prices.
From what I have seen and read of New Vegas its a must have for any Fallout fans out there!
I'm not sure exactly when the expiry date is but it is a weekend sale so I would have to guess it will finish Monday afternoon sometime for us.
EDIT:
Team Fortress 2 is also on sale this weekend for just US9.99! http://store.steampowered.com/app/440/ Thats half price for a fun multiplayer game!
what the hell is "steam" anyway? I'm too lazy to look it up myself, can someone please tell me?