Best of the Web
For a guy born 700 years before the birth of the Internet, Dante has a great presence online. This site from Columbia University is a clean, comprehensive introduction to Dante's life, works, and times. Helpful links direct you to other places on the Web with information on Dante and the medieval period.
This gorgeous site from the University of Texas at Austin is essentially an illustrated, online, annotated version of the Divine Comedy . Though there are many places on the Internet devoted to Inferno, this site gives equal weight to Paradiso and Purgatorio. It's also beautiful and easy to use and understand. Go Longhorns.
It's the Divine Comedy like you've never seen it before. This site is incredible, offering you choices on everything from which translation to read to the ways you'd like the page annotated. Would you prefer your Commedia illustrated by Botticelli, Dali or Dore? Just click. Dante couldn't have predicted this.
The Dartmouth Dante Database is attempting to put the texts of all the commentary written about the Divine Comedy in the last 700 years online. It's not the easiest website in the world to use, but it's an incredible resource if you know what you're looking for.
This site maintained by Carlo Alberto Furia is a simple introduction to Dante. He does a great job of summarizing the complex politics of Dante's time. It has galleries of art, texts, and fun facts related to Dante.
Fordham University maintains this incredible online library of all things medieval. There is more information at this site than you will be able to deal with, but it is an extremely useful study guide to the Middle Ages.
Georgetown University's online medieval library is a fun treasure trove. You can search their vast online archives by subject—such as feudalism or magic and alchemy—or by the type of subject you're interested in. It's also a helpful study aide, particularly for longer projects.