How can I use mixins or modules in my controllers in Rails 3?

I have some behavior in my controller that I pulled out into a module in order to test better and re-use it in a few places. Two questions about this:

1. Where is a good place to put my modules? They need to run in order to be available to the controllers, so I was thinking the config/initializers/ directory. That seems a little suspect to me though. lib/?
2. How do I ensure the code gets run so the modules are available to include in my controllers?

Thank you kindly sirs.