Free books and papers
Books
http://poiskknig.ru Electronic books search
http://us.geocities.com/alex_stef/mylist.html Math books
http://www.lib.org.by/_djvu/M_Mathematics/ The library of scientific literature
   
Papers
http://arxiv.org/find/math ArXive
http://www.maths.abdn.ac.uk/~bensondj/html/maths.html Dave Benson's Mathematics Links
http://gdz.sub.uni-goettingen.de/index.php?id=2&L=1 GDZ
http://www.digizeitschriften.de/no_cache/en/home/open-access/browse-journals/ DIGI Zeitschriften
http://www.iop.org/EJ/ IOP
http://www.numdam.org/?lang=en NUMDAM
http://projecteuclid.org/ Project Euclid
http://www.mathnet.ru/ Russian journals
   
Non-free papers
http://www.jstor.org/
 JSTOR
http://www.ams.org/mathscinet/ MatSciNet
http://www.zentralblatt-math.org/zmath/en/ Zentralblatt
   
Miscellaneous
http://eom.springer.de/
 Encyclopaedia of Mathematics
http://www.jmilne.org/math/ J.S. Milne's homepage (Number theory resources)
http://www.warwick.ac.uk/~masda/ M. Reid's homepage
http://hep.itp.tuwien.ac.at/~kreuzer/CY/ Database of polytopes
http://malham.kent.ac.uk/grdb/index.php Database of toric varieties