When my playing/inspiration hits the wall, there are a few things that I use as a kick-in-the-ass-by-a-giant-boot. Finding something new and fresh, prefferably major sounding, different from what I'd been playing lately; any form of meditation(I believe that almost anything can be performed in a meditative manner, like walking, swimming, house-cleaning,...); a guitar freak concert, anything from classical to metal; playing other instruments breaks the guitar-induced habbits; drawing inspiration from other arts, even martial; playing WITH the guitar, like a baby I am, with everything I might think of (actually, I do that for fun all the time).
Oh, yeah, getting high sometimes seems to help me too, not that I advertise it.