To be honest, I don’t really like Silverlight apps, but Tagxedo is truly great.
Just enter a website’s url (or just plain words) of your choice and it will generate a cloud for you, based on its content, as shown in the image below.
Variable parameters include font size, color, alignment and shape.
The app itself feels a bit buggy and the export-to-png didn’t work quite properly for me, so I had to take a screenshot instead, but still, the idea itself it brilliant.