I think we've all been there. It's not unusual to hit a dead zone and the posts here have had some great suggestions. Here are some things that (sometimes) work for me when I go totally flat.
1. Switch formats. Shoot MF for awhile instead of 35mm. Or Minox. Or LF.
2. Switch from B&W to Col. Try something new, like Velvia.
3. Shoot some Kodak HIE infrared.
4. Shoot with a Holga.
5. Shoot with a small, carryaround digicam (you needn't even save any of the images, but it allows you to experiment like crazy, which can stir up the creative juices)
6. Document your home town. Nothing fancy, just pictures of streets, buildings (even gas stations and groceries), street lights, landmarks. In 10-15 years it's astonishing how interesting these shots become when things have changed.
Sometimes I don't even try to get out of my rut. I switch to gardening or cooking or reading and just wait until the photo urge returns.
Gene