Leave it to the new Borderlands 2 DLC, Tiny Tina's Assault on Dragon's Keep, to throw in at least one more good reference for the road.

The shout-out here is somewhat more substantial than an easter egg—as documented by Gamefront, it's an entire quest dedicated to Dark Souls. (Insert joke about difficulty here.) I haven't played the new DLC yet, but I'll keep an eye out for this one.