https://github.com/heroku/heroku-pg-extras - IF you use heroku, install this to look at cool stuff.
http://mikepackdev.com/blog_posts/40-5-early-lessons-from-rapid-high-availability-scaling-with-rails - A neat blog post about scaling ello from 0 - 100
http://rny.io/rails/postgresql/2013/08/20/postgresql-indexing-in-rails.html - a good blog post with good/real examples