Whether you've decided to watch the entire run of Babylon 5 for the first time or the fourth time, you'll want to visit The Lurker's Guide to Babylon 5.
I recommend reading the guide entries for each episode after you've watched them because they contain interesting commentary and questions. Plus quotes from JMS (creator/producer/writer for the series). Of course you'll want to wait to read the entry for the pilot movie 'til after you've watched both parts of it, lest you encounter some spoilers.
Anyway. The whole run begins again tonight on the Sci-Fi channel with the first part of the pilot movie. Letterboxed! Episodes air weekdays at 6pm central time.