One of the first decent lenses I ever got was the 50mm f2.8 Sigma EX Macro lens. Being a primes lens and part of Sigma’s professional EX range, this lens is sharp. It was also outstanding value for money. I think I paid about £170 for it. The lens allows you to take 1:1 macro photography. Here are two samples I took using it.
My only criticism, if that is the right word, is that with this lens to achieve closeup macro shots like the ones above you need to be right in there. The barrel extends right into the scene and for both shots I was literally about 2cm away. This is fine for still life flower shots but a lot more difficult when trying to capture moving objects. Sigma do have longer telephoto macros lenses that might be more suitable for this type of application but I have yet to use one.