Well, the best macro lens for the Rebel is probably the EF-S 60/2.8 macro
. Macro lenses have flatter fields plus higher resolution and contrast than normal lenses when close focused, especially at wider apertures. They also provide higher magnification.
That being said, if you're shooting stopped down in order to get adequate depth of field for 3D subjects, then a lens like the 18-55 isn't so bad and you really might not gain all that much from a dedicated prime macro lens. If you're happy with what you have, I'd stick with it for now and look for a better lens only when you become unhappy with the results from the one you have!
The EF-S 60/2.8 macro can also double as a rather useful portrait lens. It's the approximate equivalent of a 100mm lens on a full frame camera and is ideal for "head and shoulders" type portraits.