Have you tried Wordle yet? It's an entertaining way to spend a few minutes or hours. Copy and paste a block of text, or type in some words, and Wordle will make a word cloud from them. The number of words, font, color scheme, and layout of the cloud can be manipulated.
Here's a cloud I made from Prairie Bluestem of May, 2008.
This one is made from the blog tags I use on Prairie Bluestem.
I didn't limit the number of words, so these clouds are large and crowded -- just like my blog.