I may be behind the times here, but I just discovered http://www.wordle.net
, a website that generates a visual representation of the frequency of words in a given text. It is very easy to use: simply copy the text you want to use (I copied the example below from The Latin Library), then click "Go". After you have created the word-image, you can play with fonts, layout, and colors.
I'm not sure how useful this is for intense Latin study (due mainly to the fact that it doesn't give you an itemized list of the words put in, nor does it tell you how many times they come up), but I think that for visual learners it could be quite effective. The principle of a wordle is simple: The more times a word comes up in the given text, the larger it appears in the word-image. It does not provide any definitions, but I think it could point you in the right direction if you were looking to generate a vocabulary list for a given author.
The following example is one I created based on the first five chapters of Sallust's De Bello Catilinae
(of which only 150 words are displayed): http://www.wordle.net/show/wrdl/6562634/Sallust
If nothing else, it's fun!