I thought I post the recent room acoustic treatment I did to my mixing room so those who, like me, don't have unlimited funding and might find some trick I used useful to them. The recent discussion I had with Valley brought this on, but I can't find this post anymore.
The most obvious problem that plagued my room was a total lack of stereo imaging, a problem I assumed to be related to the reverberance of the smallish room.
I chose to tackle the problem three ways: first, to cut down on the floor to ceiling reverberation I was to add carpeting; next, for the parallel wall I was to use sound absorption material of some kind and thirdly I needed to tackle the room corners problem.
So, for the carpeting I chose one of them commercial carpet available in big renovation center as I wanted something that was cheap, durable and not too thick with a discreet design. I paid less than a dollar a foot for carpeting, which is extremely durable and which I installed myself BUT, you need to add an underlining to those. For underlining I used the lining which is used in new condo for sound deadening, http://www.dura-son.com/, not exactly cheap but easy to install and extremely efficient and available everywhere.
Next came the wall-to-wall reverberation problem. I first looked at product specifically made for this task like Auralex product, but those product were extremely expensive and I couldn't find them anywhere but online; I would never buy product of this type online so... Then, while browsing the isles of my favorite renovation center I found theses 1 foot square tiles by about 5/8" thick made of cork; at only about $1.00 a square foot I quickly bought a few pack and made some test. Wow, those are extremely efficient to the point of completely deadening the room if you use too much of them. After some testing I decided on a pattern and glued them on. this is what it looks like (sorry for the bad photo):
Lastly came the corners problem. I just used some crown molding that I installed in all the ceiling corners; the one I used, because I'm a cheap bastard, were the MDF kind and looks good once painted.
Total cost for a 140 square foot room: around $400.00 CDN (about $300.00 US).
Result:
The first thing really, and I do mean REALLY, obvious is the stereo image that hit me full face; Wow! I then listened to some classical recording; again WOW! I could hear some instruments, in recording I knew, that I've never even heard before, it was a totally new listening experience. Is it perfect? Probably not, but the improvement is a thousandfold, even considering the small cash outlay. I do plan to take some measurements later this year and probably tweak it some more, but for the time behing it's certainly something I can live with.
If you have a studio that's worth a quarter of a million dollars, just disregard this post, but others might find something useful somewhere in there.
I've got rather nice 2-way hifi speakers, but they don't image nearly as well in their current location as they did in the shop. I should invent something movable behind the speakers to cover the mirrors. Movable as it's also our living room and our clothes are in the closet. And this on a budget... 
They're certainly no use for soundproofing!