The series ran for 5 seasons with a 5 year story arc. This included a 2 hour pilot episode, 110 regular episodes, 5 made for TV movies, A 13 episode spinoff series (Crusade) and a recent direct to DVD release.
A full chronological episode list can be found on The Lurkers Guide to Babylon 5 which at one time was the ultimate source of all information relative to the Babylon 5 universe.
All of these have been released on DVD but most if not all these can be viewed on line. I have not however been able to find a solitary on line source for all episodes and movies. Some can be found on Youtube. Some seasons are on the WB web site