Here’s a useful tip mentioned in one of the sessions at AWS re:Invent this year.
There is a little known API call that lets you query some of the EC2 limits/attributes in your account. The API call is DescribeAccountAttributes and you can use the aws-cli to query it from the command line.
For full JSON output:
aws ec2 describe-account-attributes
To query select limits/attributes and output them in a handy table format: