I just put together a very simple calculator to show the equivalent focal lengths of lenses across a variety of sensor sizes/film sizes. I also added the ability to enter your own crop ratio to calculate any missing film size. There's a number of these online, but I haven't seen any with the formatting I wanted to see, which this is. My next steps with this is to add photos with cropping lines to give it a more visual element.

http://taishimizu.com/index.tai?view=lenscalculator

PS- I keep getting errors trying to post this, does anyone else experience that a lot when adding new topics?