None of the current crop of Dslrs are "cheap and nasty" they are all competent in their own way. You have to make the decision of cost vs performance, budget vs cost, image quality, noise, ergonomics, etc, etc. Like Michael said, put your hands on the different models, navigate their menus, take some pictures, "feel" them.
I could tell you the 20D is probably the best of the mid priced Dslrs, the Rebel XT is the best value for the price, the D70 has a solid legion of fans, the *stD is an excellent value, the Sigma SD10 has the most interesting sensor, etc, etc. But that is not my place. You have to make the ultimate decision. Review sites like DCresource and DPreview are excellent sites to gleen information and bring all of these choices into focus.
http://www.dcresource.com/
http://www.dpreview.com/
The D70S is more of a firmware update than a new camera. The only physical difference between it and the D70 is a larger LCD. You would do better value wise by purchasing a D70 and upgrading the firmware, Nikon is making the new firmware available to all D70 owners. That being said, the D70 would be somewhat of a natural choice for you, you are already a Nikonian, and you should be able to use your current lenses on the D70.