I've been spending some more time lately with a Panasonic Lumix GF1 and the 20mm 1.7 pancake lens. It's an amazing combo--and great for street photography. Lightweight, flexible, and great quality photos. It could perform better in low light although still gives usable results till at least 1600 ISO (and then you still have the 1.7 aperture to work with).
The shot above is one of my latest subway shots. For more samples, run this search string on my flickr account.