One of the most important tools for teaching any content area is setting events in time. A timeline can be used to depict actual dates and times for biography, history, story lines and anything else you can think of. You can also use a timeliner tool to depict fractions and decimals in math.

There is a software piece called TIMELINER, however, you can also use any of these Web 2.0 tools to create timelines. Try one!
Timelines.com - http://timelines.com/
Online Timeline Maker - http://www.teach-nology.com/web_tools/materials/timelines/
Interactive Timeline from ReadWriteThink - http://www.readwritethink.org/materials/timeline/
xtimeline - http://www.xtimeline.com/
TimeGlider - http://timeglider.com/ Timeglider seems to have some pluses for school use. (Unique URL that must be distributed by you.) Check out the instructions.
Dipity - http://www.dipity.com/

Need data for your timelines? Try:
Want to see some already created timelines? - http://www3.canisius.edu/~emeryg/time.html