Tag clouds are a great way to show word density and are most commonly found on blog websites or search engines. The larger the font the more often a word has been used and are good way to see the trends over a certain period of time.
See what happens when tag clouds are used to visualise the public speeches of every American president since John Adams in 1797.
As you would expect the density of certain words change over the years to match the situation of their times. The word communist is used a lot during the 50’s and 60’s whilst the word Terrorist is a more recent addition and is used a lot by George W Bush.