Document Sharing Sites: 

http://SlideShare.net
http://Issuu.com/
http://Pdfcast.org/

Ebook Directories: 

http://Free-Ebooks.net
http://E-library.net/
http://EbookDirectory.com/
http://www.E-booksdirectory.com/
http://Ebook88.com
http://Ebookjungle.com
http://Drewsebooks.com

Question & Answer Platform:

http://answers.yahoo.com/    
http://www.Allexperts.com 
http://www.Answerbag.com 
http://www.aolanswers.com 
http://wiki.answers.com/