Left 4 Dead 2 PC and its four-pack bundle have been marked down by half on Valve's digital distribution platform Steam, bringing down their prices to $24.99 and $74.99, respectively. That particular offer runs until Thursday, March 25 at 4PM PST.
Meanwhile, Amazon.com is today and today only offering L4D2 PC at $23.99--52% off, though you'll have to wait for your copy to arrive instead of just downloading it from Steam--and the Xbox 360 version of L4D2 at $33.99, a discount of some 43%.
Speaking of four-packs, that of Battlefield: Bad Company 2 PC has reappeared on Steam, offering four copies of the shooter for the price of three ($149.97) until April 2. Thanks to Shacknews community members Gummy Joe and trineas for the heads up.