If you're looking specifically for a rangefinder camera – in that you do not look through the lens and use a split-image mechanism to match subject distance to the plane of focus of the lens – with a digital sensor, the only ones available are the Leicas (M-E, M and M9 with some minor variants). Although they are likely to go down in value over time (like almost all digital cameras), those are probably outside your budget.
If you're looking for something that looks like a Leica but isn't necessarily a rangefinder camera, probably the closest current camera is the Fuji X-Pro1. It is similar to a digital Leica M in the following ways:
- It lacks a flipping mirror mechanism
- You do not look directly through the lens to compose; instead, you look through a viewfinder with overlaid frame lines
- The X-Pro1 looks an awful lot like a film rangefinder camera
However, the X-Pro1 has the following differences from the M cameras:
- The X-Pro1 uses Fujifilm's new X mount, while the M uses the long-established M mount.
- The X-Pro1 has a "hybrid viewfinder" that overlays an electronic preview in the viewfinder.
- The M9 or M-E or older have no sort of "live view" that allows you to compose with the digital screen instead of the viewfinder.
- The X-Pro1 has autofocus, while all Leica rangefinders are manual focus only.
- The X-Pro1 has an APS-C size sensor (like most digital SLRs), while the M9 or newer, M-9, and M-E have a larger 'full frame' (roughly equivalent to 35mm film) size sensor. The M8's sensor is in between those two sizes.
Fujifilm also has the new X-E1 (similar to the X-Pro1 but uses a fully electronic viewfinder instead of a hybrid viewfinder) and the X100 (with a fixed 35mm equivalent lens instead of an interchangable lens mount.
If interchangeable lenses are important to you, you might also look at the Olympus Pen series, the Panasonic GF/GX series, or the Sony NEX line.
Like the Leica, these cameras do not have a reflex mirror and are part of interchangeable lens systems. Unlike a Leica, they use some sort of electronic viewfinder or you compose using the digital screen on the back. Also, all of these cameras have autofocus.
If you specifically want the experience of using a rangefinder but can live without an actual digital camera, you could use a film rangefinder and then have the film scanned. Leica and Cosina (using the Voigtlander and Zeiss brand names) still make new film rangefinders, and there are many available for on the used market.