Very reasonable prices:
http://www.atsacoustics.com/
Just wanted to 2nd the ATS recommendation (for acoustic tiles at least, not bass traps). I just hung 60sq feet of acoustic tiles from ATS two weeks ago. Very fun and a bit embarrassing that I waited so long on this upgrade - as it has made a huge improvement considering the small cost.
If you don't have room treatments get them... ATS even has an online calculator to guesstimate your current and target reverb times.
Bass Trap Question - in my listening room (aka livingroom...) I have a decent size coat closet in the back corner. Could I swap the door out with a backless and framed acoustic tile to create a bass trap? Maybe even fill some of the closet space with insulation or something?