General
Theme support plugin for rails
Another area I was having trouble with in Rails and found a simple plugin solution - switching layouts depending on whether you're logged in and which theme you've chosen if you are. Matt McCray comes to the rescue with his Rails Theme Support Plugin. It allows you to have multiple themes in their own sub-directories and only having copies of templates that actually differe from the application default - if there's no theme-specific file it'll just use the default one. It also has Liquid templating support, though that's not something I'm using at the moment. Might come in handy in the future though.