DocJax

DocJax is a new site (beta) for searching for documents/eBooks (PDF's, XLS, etc) Once you find the document you can either preview it in the web, rate it, or download it.

What makes this search engine so great is the Web 2.0 features. You can create an account then rate documents, post comments, chat, etc. So far, this has been the best way to search digital content that I can find.

For more info click here.

Below is a pic of a search result, notice how you can preview, rate, or download.