Just returned from Cheltenham Camera Club, where we had a presentation of photographs & slides as follows:-
Nature as I See it ....presented by.....Terry Bickley. DPAGB FDPS ARPS BPE2
Some great macro photography & having spoken to Terry, he reccomends the
Sigma 105mm Macro 
He has the rest of the range of macro's but swears by the 105mm. Looking at the quality of his shots, if I had to choose a macro lens.....it would be this one.