Google chrome have just released a BETA version of the extension gallery. You can check it out here. There are many good extensions already released. I have listed below some of the more interesting ones.
Speed Tracer (By Google) is one of the more advanced extensions available, this will provide you with detailed graph analysis of the speed that web pages are loaded.
Speed Tracer is a tool to help you identify and fix performance problems in your web applications. It visualizes metrics that are taken from low level instrumentation points inside of the browser and analyzes them as your application runs. Speed Tracer is available as a Chrome extension and works on all platforms where extensions are currently supported (Windows and Linux).