When I get given a new Mac by work, or buy a new one for myself, I always follow the same steps to setup my system for fast development.

 Install the following:

• Homebrew, You do need to install Xcode first:
• * Xcode - my personal preference, but I use a lot of its features.
• * Or GCC - which is an open source and much faster to download alternative to Xcode.
• Sublime Text, with these plugins:
• * Sublime Package Manager
• * SublimeLinter - I've got a write-up of how to install this, which includes a nice file settings of settings I use personally.
• Alfred - An excellent replacement for SpotLight
• Total Terminal - Extremely useful in my day to day development.
• Growl - It's always nice to know whats happening (redundant if you have Mountain Lion)
• DotFiles - These are my preference. If you find yourself making changes to your own liking, branch :). Remember to push anything back, which you think is a good addition to the repo.