roei z
Veteran
Have you considered the Panasonic/Leica 14-50mm zoom? It seems to have all the features you want: f2.8-3.5, auto-focus, Optical Image Stabilization, and an aperture ring on the lens:
http://www.amazon.com/Panasonic-14-50mm-2-8-3-5-Four-Thirds/dp/B000PCS1NG
i have it it's great. already posted about it.