Rails, TDD and Lean Startup is the magic triad for me that is much more powerful and any of the constituents alone. I deeply believe that:

• Ruby and Rails produce a 10x developer productivity gain, because of: (a) its focus on developer ease of use; (b) convention over configuration; (c) the vibrant open source community around it
• TDD creates 10x better code and applications, because it (a) drives looser coupling and better coherence; (b) removes the fear of things breaking from the developer and thus unleashes their productivity and creativity.
• the Lean Startup model makes 10x better companies and products, because (a) a lot less time is wasted building things nobody needs or wants; (b) team members are empowered to make actual product changes that have impact on a daily basis
• Focusing on the team creates a 10x better company culture with lower attrition and higher productivity, because in the knowledge economy, people want (a) a sense of autonomy of who they work with and what they work on; (b) a sense of mastery to learn something deeply and develop their skills; (c) a sense of purpose in their work. (Source: Drive by Daniel Pink)

I'm a consultant, developer and trainer in San Francisco and I feel lucky that I get to do all of the above most of the time.