Is there a good way to implement a nested form in Rails 3?

First, you'll want to check out our Ryan screencast: http://railscasts.com/episodes/196-nested-model-form-part-1

Once you've seen the tutorial, you'll want to play around with the nested_form_for gem: https://github.com/ryanb/nested_form

If you need to see it in action, I've made an example of a working carrier + nested form here: https://github.com/galaxylord/carrierwave_nested

You can also always pull guides by guides for some examples: http://guides.rubyonrails.org/routing.html#nested-resources

Hope this puts you on the right track!