I found a really cool web application - Wordle. It creates a tag cloud of words in a piece of writing, and the words that occur more frequently is bigger. This is one I did of George Orwell's novel 1984. (click on the image to see it full size)
Doesn't it look cool? You can use it to find the most important points in a piece of writing, or find which words are overused in your own writing. You can customise the font, colour and layout. You can even print them out and hang it on your wall. Here's another I made of Jane Austen's Pride and Prejudice.
Another similar web app is TagCrowd. It doesn't make designs that are as pretty as Wordle, but it does have a few more practical options, like a stop list to exclude words you don't want, grouping similar words and showing the frequency of words.