So the lovely wedding photographer I've been working with Nick Murray first introduced me to extension tubes as a cheap alternative to macro photography. At weddings there is usually only one thing you need to macro - the ring photo and for one photo sometimes it's a bit crazy to lug around a heavy macro lens. This is where the extension tubes come in handy. Essentially they are a tube that extends your own lens (fitted to the camera body before you put your lens on) allowing you to focus more closely on a subject.
Now with most camera equipment you can get the high end goods right down to the ridiculously cheap items off eBay. I personally went ridiculous cheap (under ten dollars) because I wanted to test the tubes out but after using them for a few weeks I'm definitely keen to upgrade. The set I bought doesn't have any electric contacts and therefore can't speak with the lens or camera, so you have to manually focus (which is okay because I use manual most of the time anyway) but the other bad news is that you can only shoot wide open - so you have to really nail focus. My set came with three rings but I've only been using the one - more that that and I've found the magnification just too much. My set also had this crazy silver lever you have to press down when removing the tube - I may have spent ten minutes thinking I had officially stuck an extension tube onto my camera for life!
For a few dollars that's not a bad shot to get :) I have been playing around with Nick's high end macro lens as well and it's beautiful and definitely in a different league to the tubes but if you want a cheaper solution and one that is easy to carry around I definitely recommend getting yourself some of these :)