A couple of interesting tools I've run across for EC2 and S3
EC2 Firefox extension - allows you to manage your EC2 instances in Firefox including:
- List available AMIs
- List your running instances
- Launch new instances of an AMI
- Manage security groups and launch permissions associated with your instances
AWSZone.com - EC2/S3 (entire, or almost the entire AWS platform actually). Very cool way to query AWS APIs via a web UI