If you use Amazon AWS EC2 instances for any length of time and do not know about or use reserved instances you should take a look at them. Amazon will provide an instance at a reduced rate with a one time set up fee (for periods of one or three years). If the set up fee and the reduced rate totals up to be less than the regular rate over the life of the instance then it may be worth your while to use the reserved instance. There are gradations of reserved instance types based on how much/often you expect to use them so the determination of where it is worth your while can be complex but their existence is another opportunity for you to reduce your costs for compute power. The first step is awareness so take a moment to spin up your awareness a little.
More about them can be found at the following link. http://aws.amazon.com/ec2/purchasing-options/reserved-instances/