For macro your options are
1. A true macro lens
2. Extension Tubes
3. Macro filters
There is nothing equivilant to a true macro lens when it comes to quality, but the other two options are much, much cheaper. Canon makes two versions of the 100mm macro. They have the Canon EF 100mm f/2.8 USM ($400ish) and the Canon EF 100mm f/2.8L IS USM ($900ish). The L version offers IS and much better durability, but the quality is only slightly better on the L version. If you plan on shooting in harsh environments, go with the L, otherwise the other version should be fine.
Canon also offers a EF-S 60mm f/2.8 Macro USM for cropped sensor models. I have no experience with this lens, but all three are true 1:1 macro lenses so they'll all give you the same magnification. For the same magnification the 100mm will allow you to be a little farther back from the subject to allow more room for lighting and such.
If you decide to go with something other than a lens, extension tubes are the way to go. They have MUCH better image quality than the Macro filters (magnifying glasses that screw onto the front of the lens), and they're dirt cheap, and can be used on any lens.