Hmm, I don't know any shops that do rentals, but you could try contacting this Pax Velo for some information on cycling in that area: http://www.paxvelo.com/
There's also a club in Annapolis that does some weekend rides out in Davidsonville.
There are probably more shops around Annapolis (Capital Bicycle, Bike Doctor, etc.), but I can' think of any that rent.