Online Encyclopedias
http://www.wikipedia.org/
http://www.webster.com Has a cool audio pronunciation feature

Maps
http://earth.google.com/  Extreme coolness!  Must download and install, and it requires a fairly new computer with a decent graphics card.
http://seamless.usgs.gov/ Like WOW man!
http://maps.google.com Like WOW man! check out the satellite view
Of course there are http://www.mapquest.com and http://maps.yahoo.com

Hurricane tracking:
http://www.boatus.com/hurricanes/
http://www.starstonesoftware.com/eots/