I found this table that gives you all the systems that auto-bracket:

http://www.hdr-photography.com/aeb.html

The D80 is the best choice for you. It has a 10MPix sensor and a fairly recent image processor.

There was a whole family of cameras with the 6Mpix sensor used in the D40. With each generation the image processor got better but the camera got cheaper. The following cameras focus with your 50mm f1.8 and do auto-bracketing, from best image quality to worst:

- D50
- D70 & D70S
- D100

Don't buy a D100 thinking its a pro version of the D40, even though it has the same sensor. The image processor is much older so there is more noise at high ISO. But then that might not matter to you.