When I get writer's block, I look to other sources of inspiration. I'll watch a movie, I'll watch TV (esp. Discovery Channel, TLC or History Channel), I'll hit the comic shop and just browse the shelves, sometimes I'll go to the bookstore and do the same.
The best thing to do is keep, as others have mentioned, an "idea folder" on your computer. I currently have about 100 short, 1-2 page ideas written down that just sit there until I need them. Maybe I'll never do anything with them, but at least they're there when things are feeling slow as far as my creativity goes. Often I'll go randomly read one or two or forty and something will happen for me - again, it might not be developing the story I just read the idea for, but it will inspire another tangent to run with.