IAM users and billing information

    By default, IAM users do not have access to the Account Activity or Usage Reports pages. However, as account owner you can grant IAM users permission to see either or both. You can then activate access to the billing pages, and those IAM users will have access to the billing pages according to the permissions you grant. (You can deny them access to some billing information.) http://docs.aws.amazon.com/awsaccountbilling/latest/about/ControllingAccessWebsite.html

Tagging Oracle Database Instances

Instance tagging is a great way to manage and monitor instances.  It is also the way to do departmental billing and now with EC2 IAM resource level permissions a method to control the actions users and groups can perform on EC2 instances (more here: http://aws.amazon.com/about-aws/whats-new/2013/07/08/announcing-resource-permissions-for-amazon-ec2-and-amazon-rds/)

Placing tags on EC2 instances is this easy:
aws ec2 create-tags --resources i-f0ef69c6 --tags "Key=Cost Center,Value=AWS"
aws ec2 create-tags --resources i-f0ef69c6 --tags "Key=tier,Value=database"
aws ec2 create-tags --resources i-f0ef69c6 --tags "Key=environment,Value=test"
aws ec2 create-tags --resources i-f0ef69c6 --tags "Key=email,Value=thomas.laszewski@gmail.com"

To view all instances (and the value) with the cost center tag issue the following command:

aws ec2 describe-tags --filters "Name=key,Values=Cost Center"

Most monitoring and billing tools (CloudHealth, Cloudcheckr etc) use tagging to manage, monitor, and report costs and usage.

AWS usage, billing, and reserved instances

ICE is an open source utility from Netflix that allows you to track AWS usages, billing, and manage efficient use of AWS:
http://techblog.netflix.com/2013/06/announcing-ice-cloud-spend-and-usage.html?m=1

AWS resource tagging

Tagging of resources is great for billing and managing your resources. You also need to be aware of the EC2 and networking services and resources that do not support tagging:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/Using_Tags.html#tag-restrictions