I've been waiting for the long promised - but not yet delivered - Oly 100mm macro and for the moment am prepared to go on waiting. However the Oly 50mm macro has superb write-ups and would I think be fine for still life. If you are going to buy an Oly lens check out BHphotvideo in the US. For some reason Oly US prices are way lower than the rest of the world and even with shipping and tax there is still a substantial saving on some lens - their 50-200 is currently half the price of a UK copy and I look longingly at at the 300mm F2.8 which is less in $ than £ even before the conversion.
I digress. Even with our Oly x2 sensor the 50mm may be a bit short for bugs so either the Sigma 105 or 150 are probably the most popular. Certainly the 150 is very well like on all the UK bug sites.
Best advice as always is go down the camera store and try them out on your camera against the sort of objects you want to photograph.