Which Dslr supports multiple exposures?

I would like to buy 1 dslr which supports this mode. Either Nikon or Canon would do.
I don't know whether canon 600D & 60D supports this mode.

Just about any proper image editing software can achieve the same result, by combining two independent photos into one. Therefore you'd be ill advised to choose your camera based on the availability of this particular feature.

Dunno about the Canon lineup but my D300 does it.

The Pentax K-30 allows for in-camera multiple exposures as does the Olympus E-30. This site lists all digital cameras that allow for in-camera multiple exposures:
http://www.neocamera.com/search_camera.php?multipleexposure=1

Note that exposure compensation is needed for shooting double/multiple exposures.

Two Exposures = 1 stop underexposure

Three Exposures = 1.5 stops underexposure

Four Exposure = 2 stops underexposure.

The easiest way is to shoot in Aperture Priority and use the EV (Exposure Compensation) Dial on your camera.

These were made with my film camera in aperture priority and its EV set to -1:

My Nikon D90 will for sure. Oddly enough, the spec sheets at Nikon do not indicate this feature (even on the D90), it so it is a fairly minor feature.

Not sure if any other Nikon DSLRs do or not.

I totally agree with Jens.

It is much easier to do in post processing, you have way better control and more options.

Straightforward, none.

Digital only allows one shot per frame. Whatever trick is done out there basically combines two or more frames into one. Some do it in-camera but the better way is to do it in the computer for more control.