For Brew driven MAMP with Apache2, PHP 5.3 and MySQL 5.1
If you've MacPorts install - you probably should move it to avoid any unintentional conflicts.
Install brew (assuming that you have Xcode installed).
$ ruby -e "$(curl -fsS http://gist.github.com/raw/323731/install_homebrew.rb)"
Install git and bash completion. (Perhaps by first following gem instructions at http://wiki.github.com/mxcl/homebrew/gems-eggs-and-perl-modules)