Books
My favorite source of inspiration is books. Reading them conjures vivid images that burn themselves into my mind. I suppose there is more to life than reading books. Someone has yet to convince me of that though. ;)

Book topics that I have found helpful:

• Fantasy and Science Fiction
  Fantasy and science fiction can be thought provoking. Seeing what other people create with their imaginations is interesting.
• History
  History contains many interesting facts if you travel off of the beaten path. Looking at the same historical events through the eyes of opponents is also interesting.
• Mythology and Folklore
  Many stories reach back to mythology and folklore as their foundation. Different countries will have similar, but not identical stories. I like reading two or three versions of the same tale. It shows you how retelling a story changes it. Creating distortions based on retelling can be fun.
• Cultural Studies
  Studying different cultures helps you to know what each culture deemed as important. Most societies have something that they consider important as a whole. It can shape villages, cities, states, and even nations.
• Languages
  Speaking a different language involves understanding a different thought process. The way a language uses possessive or deals with gender can teach you some things about the people who use that language. All right, the depth that you would have to go into for learning a language to be helpful might be a bit extreme. Learning languages is fun though. :)

On-Line Research
If I am floundering for idea on an area I am in the midst of building, I get a quick fix by researching the area on-line. There is a wealth of information available on the web.

Your Mud's Map
Look at your world's map. There are always gaps that could be filled in. If your world does not have a map, work on sketching one out. It may help you notice holes and inconsistencies in the world. There is always something that needs done. While it may not always be awe-inspiring to start off with, doing something that needs to be done can be enough to get you over a block.

Music
Certain sounds inspire thoughts and feelings. The haunting sound of the flute sets my mind adrift. Lyrics often tell short stories that can be interpreted and expanded upon.

Artwork
Think of artwork as a moment frozen in time. Something happened to cause that moment. Now thaw the moment. What happens? You can create a past and a future for the piece of art.