Center for Disease Control
An excellent government resource on what you might consider doing when traveling abroad, from possible diseases to vaccines to health care overseas.
XE Currency Converter
A great tool for converting one currency to another. It goes both ways and incudes a comprehensive list of currencies.
Maps & Guides
Detailed atlases for most states and standard
items in my travel kit since 1976 when DeLorme came out
with their first one (Maine)!
I always travel with their Map-n-Go 6.0 and Street
Atlas USA Deluxe.
Planet Guidebooks A staple in my reference library along with LP's
guidebook upgrades, snapshots of various destinations,
Scoop Travel News, and other useful information.