I've done one of these before on a different website, but here's a newer one that lets you customize a bit more. You select a bunch of text from your blog, send it to the wordle and they make this cool summary of your blog. It's interesting to see what words are used the most. I forgot to delete "posted by Becca" that ends each of my posts along with "comments", so obviously those ones came up a lot!
Go to http://www.wordle.net/ to make your own!