Calendar
MandarinTools.com - conversions between the Julian and Gregorian calendars and the Western and Chinese lunar calendars
Currencies
Bloomberg.com - benchmarked rates for the eight major world currencies
CNN Money.com - current and recent exchange rates between 17 major currencies and the US dollar
OANDA - exchange rates for 164 currencies all the way back to 1990
XE - country currency rates refreshed once per minute
Inflation Calculator
The Inflation Calculator - a site to adjust given amounts of money for inflation according to the Consumer Price Index, from 1800 to 2007
Language Translation
Google Language Tools - translations of phrases in one language to another
Word2Word - dictionaries and translation tools for over 100 languages
Lengths and Distances
Length and Distance Conversion - a tool to convert units to meters, yards, feet, inches, miles, kilometers, leagues and fathoms
Speed
Online Speed Conversion - a tool to convert speeds to mph to kph, mph to knots, mach and speed of sound
Temperatures
Online Temperature Conversion - a tool to convert temperatures to Celsius, Fahrenheit, Kelvin and Rankine
Time Zones
The World Clock - a tool to convert time in one world region to another and identify current times in all areas of the globe
Travelmath - an online calculator to convert time in one world region to another, and to determine time and distance between two points on the globe, by plane and by car
Weight and Mass
Weight and Mass Conversion - a tool to convert units to grams, grains, ounces, pounds, stones, kilograms, tons and tonnes