MathSciNet is an extensive database that covers mathematical literature world wide since 1950.
ZentralblattMATH is the worlds most complete and longest running abstracting and reviewing service in pure and applied mathematics.
BrowZine (app for iPad or Android) helps you get an overview of electronic journals.
You can find the desktopversion here.
Literature search, writing a thesis, research support and other questions:
LaTeX and companions
Templates for LaTeX and Beamer at the Department of Mathematics
Martin Helsø's guide to LaTeX (Norwegian)
Information about LaTeX and BibTeX