The Theracane is basically a cane with some hand-holds, which is meant to make it easier to massage areas like your back. Experimenting in the store, I did not feel it was really suited to deep, high pressure massage, but it would still probably be a useful tool. Check out their website if you haven't seen the Thera cane before. The problem is that it goes for between $50 and $30, usually without any return policy. I've come up with a couple of $1-$5 alternatives which work pretty well.
First, you could always try doing a tennis ball massage, (just trap the ball between the wall and your body, and wiggle around). This works OK, but doesn't really make for a deep massage because the ball is too big. Also it can be difficult to pinpoint the spot you want on your body this way.
So, what I really suggest is to go to a kitchen store (I went to IKEA) and find a short kitchen tool which has a round handle, as in the picture to the right. The one I found cost 99 cents. Now, since it's not rounded on both sides, it may be kind of hard to hold comfortably, especially when applying lots of pressure. Solution: cut open a tennis ball, and stick the non-round part into it. Now, you have a nice soft handle, and a good, hard massage point. For extra force, I put the tennis ball up against the wall, and then lean into the rounded handle of the tool.
That works pretty well for the lower back. It's a bit hard to position the tool, since it's all happening behind your back, but your arms can be flexible enough to make it happen.
Much harder is to massage your upper back or neck. Perhaps you really need a Thereacane? No, there's a cheaper alternative, on the order of $5 at your local hardware store. Get a storage hook (here's one link, but it's probably better to check it out in your local store first). See picture below for a suggested model, but I'm sure you can use your own judgment on this one! It's really crazy how much you will get charged for "health related" items, as compared to everyday products that are just as good but have to appeal to the more cost-minded general consumer.