So many manufacturers... Try ASC (Acoustical Sciences Corp), RPG Acoustic Systems, Real Traps, and GIK Acoustics in addition to above for a start. Also, Google "diy acoustic room treatment " if you're handy.
The hard part isn't finding where to buy the stuff, but learning how to use it You can use the "trial and error" method, or get something like REW (Room EQ Wizard) software and work on it a little more systematically. Oh, and if your room isn't vaguely symmetrical, and is used for other things, it's a lot harder to get it just right. It'll still be an improvement.
