I tend to avoid generators and the like, as they tend to be fairly cliche in my experience.
My favorite methods of inspiration are...well, a little strange.
- Wikipedia's Random Article Button
- Opening a dictionary to a random page
- Picking a single word that relates to the theme I'd sort of like to design something for
- Browsing DeviantArt or Google Image Search for random keywords, or for whatever strikes my fancy
- Put on Pandora or just listen to random music from YouTube or my music library
I then tend to toss around the word/article/whatever in my mind until it begins to take some cohesive shape. This shape is often incredibly tangentially related: I'll just follow through any train of thought I happen to have until I start to find the edges of an idea I like.