Proceedings of all past ICM-s can be found here: http://www.mathunion.org/ICM
A nlab page http://www.ncatlab.org/nlab/show/Online+Resources contains a long list of math blogs and forums.
http://numdam.org is a collection of old issues of many mainly French math journals. http://www.mathnet.ru site has links to free old issues of most of the Russian math journals (and even some video lectures) in Russian and links to some non-free English versions. There is also an English mode of the site: http://www.mathnet.ru/index.phtml?&option_lang=eng. A smaller free depository of old issues of Polish math journals is http://matwbn.icm.edu.pl (click on the flag for English).
Max Planck maintains links to a very long list of journals, most of which are proprietary and usable only from their site, but the list is still useful because a sizeable fractions of links are also to free journals or some volumes of journals which are free, and those are mainly usable from all locations. The current URL is http://rzblx1.uni-regensburg.de/ezeit/fl.phtml?bibid=MPIMA&colors=3&lang=en¬ation=SA-SP
Many resources can be found at the sites of main world math institutes like ihes, mpim-bonn, Oberwolfach, msri, kitp, ictp, rims, ias, Steklov
AMS keeps a long list of math societies throughout the world with links to their sites, which are often useful.