Update: The codes posted earlier today have unfortunately expired. As long as Gearbox keeps posting them, however, we'll keep sharing them, so keep an eye out.
Randy Pitchford has tweeted a handful of new SHiFT codes for Borderlands 2. These codes will be active until 4 PM CDT, so you've got two hours to redeem them.
Gearbox Software's president just Tweeted a number of SHiFT codes for Borderlands 2 that should be active until 12 PM CDT.