I’ve been doing some work with Amazon EC2 the last few days. An invaluable tool is the EC2UI firefox extension that Amazon have written. This provides you with a simple GUI inside the firefox chrome which makes it really easy to manipulate your EC2 instances.
A few weeks ago Hardy moved to using firefox 3. This meant, amongst other things, that the amazon plugin stopped working. The firefox guys have a webpage up that explains how to update extensions for Firefox 3.
Update: See comments below for new versions