Nginx's easy load balancing made it an essential part of this stack. The simple implementation of an SSL certificate also helped us a lot in this stack.
Ubuntu is great because it's free, and all the free packages make creating the perfect stack easy.
Integrating Amazon's many AWS services, such as RDS, is a breeze if you're using EC2.
Using bootstrap makes standardizing our templates very easy, and navigating the site becomes smooth and loading is more efficient.
The Ajax calls you can make with jQuery makes integrating the front end with the back end very smooth.
Rails was simple to develop on, and the programming is very straightforward.
Stripe's simple API and ease of use makes it a great payment processor for developers.