Borderlands 2 for the PC is now available for digital pre-order. Digital versions aren't being slighted; they will receive goodies just like the physical version. If you pre-order you'll get access to the Borderlands 2 Premiere Club, featuring a free download for the Mechromancer class. She'll be available sometime after launch.
If you're thinking about jumping on the Borderlands bandwagon, you'll want to take advantage of this mega-rad deal: Borderlands 1 on the PC and all of its DLC at 75% off through 7/30. Steam and Amazon are supporting this offer.