The "Front for the arXiv": a good place to find recent math papers.
front.math.ucdavis.edu/

See here for corrections to Adams and Franzosa's Introduction to Topology: Pure and Applied.
germain.its.maine.edu/~franzosa/ITPA.htm

Mark Brittenham has a nice page with lots of topology-related links, including upcoming conferences.
www.math.unl.edu/~mbrittenham2/ldt/conf.html

The AMS calendar is another good place to look for conferences.
www.ams.org/mathcal/

The Park City Mathematics Institute runs a great workshop every summer for all levels, including undergraduates. If this year's theme appeals to you, think about applying!
hpcmi.ias.edu/current/program.php

Not sure about a mathematical term you came across? Try these.
www.mathworld.com
www.planetmath.org

Dror Bar-Natan maintains the Knot Atlas.
katlas.math.toronto.edu/wiki/Main_Page