For fun, I dove into this recently. The only strong opinion I have is for Rails projects to ship with Cucumber as means for acceptance testing. Here are a few good Rails projects which satisfy that.

* The Rails Dev Directory: http://github.com/engineyard/rails_dev_directory/

* Spree: http://github.com/railsdog/spree

* And Gemcutter: http://github.com/qrush/gemcutter. Gemcutter also uses Gemfile.

* Fat Free CRM: http://github.com/michaeldv/fat_free_crm. It doesn't use Cucumber, but it's still good code.

If you want to get setup with Rails 3.0, check out this gist I wrote: https://gist.github.com/50be644a99ff372d5b1f