Don't have a lot of time? Here's a short blog post with two cool tools that you can start using right away.
Online Stopwatch (www.online-stopwatch.com)
It is what it says it is. Couldn't get much simpler than this. Choose from several different types of countdowns. My personal favorite is the bomb. (Pictured below)
Create A Graph (nces.ed.gov/nceskids/createagraph)
Teach your students all about graphing. This tool lets them select a type of graph, enter their data on the form, and select colors and text styles. The final graph can be printed or saved as a PDF, JPEG, or various other types of image formats.
Here's a sample bar graph I made in just minutes...