Google Scholar - Stand on the shoulders of giants (Tracking is 'free')
Indiana University - Digital Library of the Commons
Check out the DLC to find international literature including free and open access full-text articles, papers, and dissertations.
Infomine - UC Riverside LIbrary
The Infomine is an incredible tool for finding scholarly Internet resource collections, especially in the sciences.
Internet Public Library
Find resources by subject through the Internet Public Library’s database.
Microsoft Academic Search
Microsoft’s academic search engine offers access to more than 38 million different publications, with features including maps, graphing, trends, and paths that show how authors are connected.