I have frequent problems with muscle knots in my back and have a found a few things helpful:

I lie on the floor with a towel rolled under my neck then elevate my legs by resting them on a chair or the couch. Sometimes I take a small rubber ball and place it under the sore spot - it hurts like heck for a few seconds, but if I move around slightly while lying on the ball, it works out the knot(s). I found a massage cushion at Bed, Bath and Beyond - it was on sale for about $80. It has a back and seat and is placed in almost any chair. It provides a pretty deep massage and can be adjusted to hit a target area or just go up and down your back.

When things are really bad, I take a flexiril, which I get from my doctor. I try to avoid that, though, because I'm sensitive to meds and need a couple days to sleep off the effects.