The only digital rangefinders are the M8, M8.2, M9, and Epson RD-1.
If you are talking about digital cameras in general, you can use your lens on any camera with a shorter flange distance than M-mount. That includes the Olympus PEN cameras, the new Olympus OM-D, the Panasonic mirrorless G series, the Sony NEX series, the Samsung NX series, the Ricoh GRX A12, and a few more I'm surely forgetting. Of course there is no rangefinder, so you will be focusing on these cameras via the LCD screen.
As to which is preferred...a lot of people here like the Sony NEX5 and 7 (well, and 3) because they have APS-C sensors (1.5x crop factor) and are also extremely compact. The Olympus and Panasonic cameras are all micro 4/3rds (2x crop factor), I think the Samsung is too? And the Ricoh GXR A12 is also APS-C.
FYI the only full-frame digital camera you'll be able to mount M-mount lenses to is the M9. Apparently if you rip the mirror out of a Canon 5D, you can use that as well...but, I wouldn't recommend it!
