Although search engines like Google and Bing provides searches for PDF files, the results might be mixed up with other links as well. Live PDF is a free web service which allows you to search for PDF files easily. Live PDF uses Google and Bing to fetch the results and users have the option to select either Google or Bing. The search results are neatly display and easy to download as well.
Search Results.
search ebooks on rapidshare and megaupload at (http://www.filerantings.com/Ebooks.html)