I have these:
http://www.bhphotovideo.com/c/produc..._Tube_Set.html They are cheaper than Canon or Kenko, but are well made. All metal fittings. Using them with my 50MM f/1.8 they work really well.
You can go with cheap metal tubes, but as mentioned you will lose aperture control and autofocus (I always manually focus when doing macro). I have a set of these too since they were $8 and I got them first.