I depends on your field to some degree. For life sciences, Pubmed works pretty good. You can also find some articles you didn't know you were looking for via sh

I depends on your field to some degree. For life sciences, Pubmed works pretty good. You can also find some articles you didn't know you were looking for via shared bookmarks on Citeulike or recommendations via Mendeley. http://mendeley.com http://mendeley.com