Don't waste your money on the Fotodiox, Zykkor and some other tube sets that sell for between $8 and $50. They are "dumb" tubes that don't have the electronic contacts allowing your camera and lens to auto focus or - worse - for you to change the aperture easily. There's a work-around, but it's a real pain in the arse just to change the aperture. Alternatively, you're stuck with shooting wide open all the time.
Like most things in life, you get what you pay for with macro tubes. Go really cheap and you'll get really cheap. Spend a little more and you'll get something that's much more fully functional.
At the cheapest, look at the Zeikos tube set, which does have the electronic contacts and usually sells for around $100 US. These also sell under the Pro Optic, Vivitar, Cowboystudio, and some other brand names (and sometimes are ridiculously overpriced). They considerably are more plasticky than the Kenko, but will still allow full function of your lens.
The Kenko appear to be virtually same as the Canon macro tubes. Kenko even sells individual tubes in 12mm and 25mm, same as Canon. But the Kenko tube set of three is probably the best value. It includes 10mm, 20mm and 36mm for about $180. Canon doesn't sell a set of three... they only offer the two sizes, sold individually.
Again, be careful whatever you get will work with both EF and EF-S lenses. The Kenko DG will. Canon "Mark II" will. Some of the later Zeikos will, too.