I use different lenses for different purposes. If you want to do macro I recommend the lens that is mentioned in the description (Canon EF 100 mm 1:2.8 Macro USM). But there are other good lenses, too. Depends on how much money you can or want to spend.
Myea, that's a great lens. However, as I have to buy the body, bag, stative etc this month, and I don't have much of an income due to living in a foreign country, I cannot spend that much. I guess the price range I'm looking at for my first macro lens will be around 2-300euro.