I wanted to point out this great post that has the opinion of 25 creative people on how to overcome a block. My favorite comes from Erik Spiekermann:

There are 6 strategies for this situation:

1. Avoid
Do something else, wash the car, back-up your data, do errands…
2. Think
Sit back and think about the issue, just let your mind go…
3. Research
Look up stuff, go through your old projects, but avoid Google — it takes too long to find anything useful…
4. Collect
We all have lots of stuff; there must be something in there that is waiting to be used…
5. Sketch
Drawing is great, even if you have no talent. Just visualising the simplest things makes them come alive…
6. Deconstruct
Take the problem apart, look at the parts and then put them back together…

Don’t forget to check out the comments, I found some interesting stuff there as well.