Have you tried any room treatments?

I see there are more and more comments in answer to different questions about treating the room rather than replacing gear. I wholeheartedly agree with this train of thought, but I'm wondering how many people have actually tried any treatments, and what they tried, or, more importantly what they thought was successful.

I first tried Sonex ten or fifteen years ago and was very happy with the results. Right now I have acoustic foam on several reflecting points on the walls and ceiling. I also have a panel behind the amp, and between the speakers to help dissipate vibrations within the baffels(?) if that's what they might be called.

What have you tried, and how well did it work?