There are a few actor cameos that come up in Babylon 5. However, was Bryan Cranston a cameo, or simply an early acting credit in the years before he made it big before Breaking Bad? Simply that he has a lot of credits, so I'm not sure which.
"Babylon 5" The Long Night (TV Episode 1997) - IMDb
For those who don't remember -
"Babylon 5" The Long Night (TV Episode 1997) - IMDb
For those who don't remember -
he's the Whitestar captain who Sheridan asks to go to his death, in order to ensure the Shadows get false information which will draw them into a direct confrontation with the Vorlons at Coriana 6.