Originally Posted by ssc456
The super range lenses are always very poor quality. You end up with tons of distortion, image quality that's on par with a kit lens at best, and it's incredibly slow and expensive. The only real benefit is not having to change lenses as often. If it's really worth it for that, then go for it, but don't expect to be getting a big upgrade from the 18-55 in terms of image quality.
OP: The t3i is a mighty fine camera. I suggest picking up a 50mm f/1.8 as your next lens, if you like shallow depth of field. You could even take it a step further and get a samyang 85 f/1.4 which would give you incredibly thin dof, but it is a manual lens. Overall image quality is quite impressive for the cost though.
If you want to get started with macro, my reccommedation is to pickup an enlarging lens and a set of macro bellows. Look for schneider or rodenstock lenses, 50-75mm is probably best for an aps camera. This method will give you excellent image quality, and the whole setup should only cost about $100.