Is it possible to have multiple users to manage an Amazon EC2 environment? I want to give access to several additional people to create machines on my existing billing account.
A few months ago Amazon announced Consolidated Billing. I never used it, but I think that is what you're looking for:
Consolidated Billing enables you to see a combined view of AWS costs incurred by all accounts in your department or company, as well as obtain a detailed cost report for each individual AWS account associated with your paying account. Consolidated Billing may also lower your overall costs since the rolled up usage across all of your accounts could help you reach lower-priced volume tiers more quickly.
You can try http://LabSlice.com. It's primarily for Virtual Lab Management (ie. playground environments), but may suit your needs.
Amazon just announced AWS Identity and Access Management - http://aws.amazon.com/iam/
As of right now, it's in 'preview' mode, but this will allow you to have multiple AWS management accounts.