‘Tags’ are usually single words, and the importance of each tag is shown with font size or color.
This format is useful for quickly perceiving the most prominent terms and for locating a term alphabetically to determine its relative prominence.
When used as website navigation aids, the terms are hyperlinked to items associated with the tag.
There are three nice and very popular design of tag-category cloud
Have a look at them here http://suncoin.net/cloud/
