Consortium for Educational Communication
http://cec.nic.in

Directory of Open Access Repositories
http://www.opendoar.org/find.php

eGyanKosh (IGNOU) 
http://www.egyankosh.ac.in/

Library of Congress
http://www.loc.gov

National Digital Library of India
https://ndl.iitkgp.ac.in/

National Science Digital Library (NSDL)
http://nsdl.org/

NISCAIR Online Periodicals Repository
http://nopr.niscair.res.in/

NPTEL provides E-learning through online Web and Video courses in Engineering, Science and humanities streams
http://nptel.ac.in/

The British Library 
http://www.bl.uk

UNESCO Library
http://www.unesco.org/library/

Virtual Library 
http://www.vlib.org

World Digital Library 
http://www.wdl.org