A website that will quickly allow you to figure out the crop factor for you camera/lenses. Works well; simply punch in mm size, F-stop, and sensor size and then press calculate, a second later you get your almost exact results!

Another thing I like is in the results it does a good job of explaining the crop factor and what is  going on with the crop, and does so in a way that anyone can understand; but, also links to more complex explanations of crop factors and sensor sizes.