I can recommend two projects:
If you have a single Rails app, take a look at Rubber. It s a gem that can provision EC2 instances for you, install software and deploy your app. It s based on Capistrano. There are recipes for the most common components (mysql, apache, passenger, postgres, etc.).
In case you have more complex setup (e.g. multiple apps or specific needs that aren t covered by Rubber) I recommend Chef. It does have quite a learning curve, so prepare yourself. Take a look at OpsCode to get started with Chef.