Here's the one I like using, which is set up for the RBT six-speed transaxle (or standard ZF five-speed gears, plus one). It's a simple Excel file; just click below to download it to your hard drive.
You can alter the values in green (tire diameter, gear ratios, rear end ratio) and the program will automatically calculate all sorts of things. Note that there are two pages to this program; selecting the other tab at the bottom of the sheet will take you to another page that displays the information graphically.
I have a gear ratio calculator posted on the RBT site, RBT Transmissions, that you might try -- includes graph. I'm still working out a couple of bugs (ex. with the 'submit' feature) and welcome any feedback that might help me make it more useful to experts, such as yourselves! BLT