I have an Epson gt-20000 that scans a up to 11.7x17" documents. Not cheap but you can pick them up on new egg on occasion for $800. Quality costs. Period. And yes , it works fine with win7 via USB and has rj45 for network scanning..
http://www.epson.com/cgi-bin/Store/jsp/Product.do?BV_UseBVCookie=yes&sku=B11B195011
I tend to scan just above 72 dpi for the reasons mentioned previously, and also being in the professional art field (making video games) for the last 15 years, I've sort of learned to fight the urge and to leave scans as is withou much color correction or mucking with the scanner settings. A good scanner setup properly will give an accurate and vibrant image as seen below or in my sig line; all out of the box default settings..
Another tip is to scan with the top open. The dark background (as opposed to the white when its closed) can often enhance the contrast on tougher images...