SLR Gear has testes an interesting macro lens from Sigma. The lens is called Sigma 28mm f/1.8 EX DG Aspherical Macro and is able to photograph at a very wide aperture.
SLR Gear ends up giving the a good review especially if you are using the lens on full frame DSLR camera. The lens does not offer the best sharpness and corner shading wide open, but it is better when used on a full frame camera.
Read the full review of the Sigma 28mm f/1.8 EX DG Aspherical Macro lens here.