Famed Android developer Koushik Dutta has released a new Android tethering app that doesn't require root access. It's called ClockworkMod Tether, and while this isn't the first root-free tethering app for Android (the ancient PdaNet comes to mind), Koush claims that the app is not detectable or blockable by carriers. The developer is known for creating the popular ClockworkMod recovery and a ROM Manager that makes it easy to change and backup various ROMs for Android phones.
We tested out the app today, and for an alpha product the installation is simple. After installing the desktop application, we were prompted to install drivers for our phone (drivers are only needed for Windows and are available for most HTC, Samsung, Motorola, LG, and ZTE phones, while others require a bit of digging). Once we ran the application and plugged in a Galaxy Nexus, the tethering app was installed on the phone and we were up and running. Currently the app only works over USB. You can try it for yourself at the source link, but Koush says he'll replace the app with a new version by January 7th, so it might be best to wait a bit longer.