Sometimes you've just got to step away. Don't step away too long, though, or it'll be hard as hell to come back. Avoid Playstation if at all possible, and only use the Internet for Dictionary.com and an occasional Google.com research check. Otherwise, your project's going to be late.
Two things really help me. I read nonfiction almost exclusively. For now, I feel like fiction is a waste of time--like I'm flipping through a celebrity magazine when I could have been learning something. Everything I learn has a chance of making it into a product of mine. Everything. So keep one or two books related to your subject matter near at hand. When you're stuck, read for an hour or two and see where that leads you.
Also, I've been keeping an idea "sketchbook" for most of the last year. I tend to get obsessed with little side-topics now and again, so I often write one or two pages of ideas on a given topic in my notebook. Even if the ideas have nothing to do with the project I'm currently working on, I try to trap them in my notebook. I keep it near me when I sleep, in my car when I go out, and on my desk at work. Some of my best ideas, many of which have ended up in d20 or D&D projects, came in the middle of a meeting that had nothing to do with the project at hand.
Later, when I'm stuck, I flip through my notebook and see what jumps out at me. Without a doubt, this has had the greatest impact on my writing of anything since I went to college to learn how to get serious about writing.
I always used to scoff at people who told me to keep a journal, because the fact of the matter is that I'm not really interested in deconstructing the events of my day in writing. I _am_ interested, however, in scribbling down every cool idea for a feat, a spell, or a comic (or character) that ever passes through my head.
They're not all golden. I look back at a small percentage of this stuff and wonder what it was I was thinking. But it's also fun to page through my notebooks and see where I first sketched out a map for "River of Blood," one of the first Living Greyhawk scenarios, or where I wrote all my ideas for the "Darkhouse of Saerloon," from Faiths & Pantheons.
There are literally dozens of ideas in my notebooks that will appear in products I haven't even been asked to write, yet.
--Erik