Two others to look at are Cloud Cruiser and Cloudyn. Both of these companies will analyze your use of AWS's cloud and tell you if there are savings to be gained by using a different virtual machine instance size, for example or switching off unused instances. Analysts I've spoken with recommend that if you using IaaS cloud resources to a substantial degree then these resources are pretty helpful. AWS offers some of these services itself through its Trusted Advisor program too. Check that out here:
Getting a handle on the costs for your cloud provider isn’t easy, as I have mentioned in several other posts here. The problem is that each provider has several different dimensions for its cost calculations: each component (network, compute, storage, bandwidth) is charged separately based on usage. And these prices frequently change (although at least most are going in the right direction, meaning they are getting cheaper over time).
So two entities have risen to this challenge and offer free cost comparison tools. You dial in what you think you will be consuming in terms of resources, and they will tell you which provider has the cheapest configuration.