HTC phones are really easy to unroot, because HTC provide a program called an ‘RUU’ that allows you just run the app and unroot (restore a stock rom) in a few clicks.

Download the appropriate RUU from shipped-roms.com. You will have to use the codename for your device, e.g.:

Original Desire = Bravo

CDMA Desire = Bravo_C

Wildfire = Buzz

Nexus One = Passion

If you’re not sure then just use a search engine to find it out.

You can either get the latest carrier branded version, or use one with ‘WWE’ in the name for a generic, World-Wide English build.

Once the RUU has downloaded, make sure HTC Sync is installed so you will have the correct drivers for the RUU to communicate with the phone.

Double click on the RUU file, click the button to view the readme which has some troubleshooting information in in case something goes wrong.

Follow the instructions in the RUU app to complete the unroot process, make sure that you do not unplug your phone until it says that it is safe to do so.

Troubleshooting

Error: Custom ID Error - You need to create a goldcard then rerun the RUU.

Thanks to 42turkeys for the guide!