How can I create an AMI from an existing instance-store EC2 instance?

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http://serverfault.com – (I suspect that this may already be answered somewhere, since it seems like it would be a common operation. But I can't find it, so...) I am a relative AWS newbie. I have inherited a running Amazon EC2 instance, with various items (Apache, MySQL, Sphinx, ...) installed on it and a bunch of configuration. I'd like to turn it into an AMI that I can spin up other instances from. I can't find any information on creating a custom AMI on Amazon's site - only the fact that you can, repeatedly referenced, as if to taunt me... I believe this is not an EBS-backed instance, just an "ordinary" one. (HowTos)