Best Cheap acoustic wall treatments?


I am converting a 12x20 space into a home theater and want to treat the room. The walls and ceiling are drywalled, with thin carpeting on the floor. Are there any inexpensive wall panels or the like that are available? Should I consider draping the entire room in fabric? Thanks for your thoughts.
jmslaw
Check out the RPG Profoam on Audio Advisor. They did a very good job on my room. 30 day money back guarantee if you don't like them.
some good info here:

http://decware.com/room.htm

And I like the plans for these bass traps:

http://www.ethanwiner.com/basstrap.html

Bounce over to the Asylum and do some studying up as well:

http://www.audioasylum.com/index.html
Make sure that any foam that you use is fire resistant or fire retardant. Coming from New England, those pictures of the Warwick nightclub fire (100 horrible deaths, many more additional horrific injuries) will haunt me forever!
http://www.primacoustic.com/index.html

Especially the Europa Flutter walls an 8' x 3' array costs about $220 Canadian. You get all the pieces and glue them on so you can take the 8' x 3' and use it on 6' x 6' for example.
I have some non-foamy suggestions.

How about curtains? Maybe not along the entire wall, but in certain key areas like first reflections and so on, possibly to suggest windows that are non-existent.

If you eventually put up shelving for your media that could be effective as well.

Good luck!