How do I find the right derailleur (gear-mech)? I have a 9 x 3 speed mountain-bike. The derailleur got broken (and was since lost), I'm trying to find a new one. What do I need to go by to ensure I get a good fit? The rear-casette (sprokets) range from 11 to 32 teeth (there are 9 of them). Is this enough information?

Edit

It was noted that I also need to know the make of the gear-shifter, the one I have is SRAM
You'll also need to know the manufacturer, so that the shifters will be compatible. Most likely it's Shimano, or SRAM. It should be written somewhere on the shift levers.