I know the Nook and the more recent Sony models both support viewing of PDF files, and they're quiet nice to look at. The screen sizes are still too small for something like technical drawings especially with fine point text and detailed line drawings. Basically I don't know of any products that would be truly useful, you're going to want a minimum viewing size of 8.5x11, for technical drawings unless you have really good vision.
A netbook might be an option, a 16:9 display ratio 12 inch screen will give you a viewable area of about 6x10 inches, that's useable, but there aren't a lot of tablets that fit well for a book style.
My best guess is what you're looking for won't exist for another year or two, they will make them though.