Set up Rails dev env in OS 10.8 Mountain Lion

1- Install Command Line Tools: https://developer.apple.com/downloads/index.action

(Thanks @davefp for this tip!)

2- Install HomeBrew:
http://mxcl.github.io/homebrew/

3- Install Git:
brew install git

4- Install wget:
brew install wget

5- Install RVM:
https://rvm.io

6- Install iconv:
rvm pkg install iconv

7- Install Postgres:
http://postgresapp.com

Actually, you can install Postgres with brew or manually, but Mountain Lion comes with Postgres already installed so you will need to fix this (or you won't be able to connect to your database). PostgresApp makes it easier for you, just lunch it whenever you need it.

Optional:

8- Install Pow:
http://pow.cx
This is quite useful when working in several projects, since it runs in the bg and provides myproject.dev urls (myproject would be the name of the app).