Science Citation Index Expanded(Web of Science)--Includes thousands of science and engineering journals. Especially good for dissertation-level bibliographies because it allows cited reference searching: that is, how many times an article has been cited by others
CiteSeer.ist--Scientific literature digital library with focus on computer and information science hosted by Penn State University"
WorldCat--Catalog of library catalog across the U.S. (and some international libraries)
Google Scholar--Search for scholarly publications in a variety of fields. Set your preferences for access to full text and to RefWorks citation export.