Keeping track of costs in AWS is always a top priority. That means tracking all sorts of things that you may not have had to keep track of while on-premises.
One such thing is orphaned disk images from terminated EC2 instances.
One pretty impressive feature of Lambda is the ability run python scripts on a schedule. I started using this to send our team daily reports of detached volumes to help cut down on costs.
The code block below can be run in Lambda with a few slight changes. It'll use SNS to send a group of subscribed users an email after each run with a list of the volumes, the size of each one and the date it was created. If you really want to get fancy, you could add a tagging mechanism to skip over volumes you intend to save.
Disclaimer: I'm no programmer - I'm a normal, every day Ops script jockey. If you have any recommendations for the code, please let me know in the comments below.