DigiKey site has lots of tools
My company, Industrycortex.com helps solve this problem for hundreds of thousands of people per year. One of our major users is the www.DLA.mil who buys all of the technical products for the different divisions of our military.
We also offer custom search engines and directories so that you can search only through your pre-approved suppliers. An example of this can be seen at customcortex.com Please feel free to contact me if you are interested in a custom search engine, directory of suppliers, or a catalog/sourcing tool for your company.