chobit

Check out the Tamrac Velocity Sling Bag.  That's what I use, and I like the fact that it open fromt he top, so you would never need to take the bag off your shoulder.  They have diff. sizes, so check out which fits you the best.

http://www.google.com/products/c ... s_upl=&bav=on.2,or.r_gc.r_pw.&biw=1920&bih=1001&wrapid=tljp131365004794920&um=1&ie=UTF-8&tbm=shop&cid=8955437403108346614&sa=X&ei=hrVMTtGyG-_SiALN_tRt&sqi=2&ved=0CH4Q8gIwBg#