In no particular order.

Firefly Talk: http://www.fireflytalk.com/

The Signal: http://signal.serenityfirefly.com/

Escape Pod: http://escapepod.org/

Various podcasts and podiobooks by Mur Lafferty:  www.murverse.com

Ask a Ninja:  http://www.askaninja.com/

The Bitterest Pill:  http://www.danklass.com/pill/

Radio Free Burrito: http://wilwheaton.typepad.com/

Tales from the ‘Verse:  http://www.talesfromtheverse.com/