Cloud Services just launched Cloud Studio which is a java-based desktop application for managing images and instances in Amazon's EC2. I've yet to try it, but from the screenshots, it looks really nice. I'm not sure, though, if it does anything more than the very capable Elasticfox which runs right in your Firefox browser. Cloud Studio is also available as an Eclipse plugin which is really convenient for Java developers and users of the popular open source IDE.
GUI's like Elasticfox and Cloud Studio make working with Amazon EC2 really easy. Now I wish someone would create similar management tools for Amazon's SQS and SimpleDB. I'd like to be able to list, see stats for, and manage my SQS queues and SimpleDB domains, items, and attributes without having to run command line scripts. Hint, hint, Cloud Services!