If you want manual focus/aperture/speed and a Leica lens the best option is a Leica X1, but it's about twice your budget. It's a brilliant camera though, with a fast prime 24mm lens and a huge sensor for such at small camera (APS-C sensor). It's about a third of the size of the Leica M that I carry around, if you remember how big that is - I can bring that to the meet. It also has the options (unusual for a prime-lensed Leica) for automatic focus/aperture/speed or any combination of the three.
Some pics taken by it (randomly from flickr)
Another option is a micro four-thirds camera like the Lumix GF1 that andrewparker suggested. There's a few Leica lenses available for it, but the sensor isn't as big as the APS-C sensor in the X1. It is about half the price though. I've not used one before, but I don't think it has a manually-settable aperture or speed, but you can manually focus the lens through an electronic viewfinder.
Just some thoughts. I'd spend the extra on the X1 myself (having played with one, it is a seriously lovely and beautiful piece of kit), but I'm a bit less sensible with my money than some