FeedVis [jasonpriem.com] is an online tag cloud generator with some additional interactive features. Users can select specific time periods, common blog themes or individual blog feeds. Individual tags can be further explored to read specific blog posts of interest.
Tags are ordered by frequency and frequency change. Frequency denotes how many times a word is used per 1000 words. Frequency change measures the difference in frequency as a percentage: greener words are unusually popular; redder words are the opposite.