Install OS X open source geo, starting from scratch. Tested on fresh install of OS X 10.8.

osx_osgeo_install.sh

#!/bin/bash

# Mac OSX 10.8 geo setup script 
# loads geo stuffs, mostly through homebrew

###################
# Before running:
#   - Install Xcode from the Mac App Store.
#   - Install the Xcode Command Line Tools by opening Xcode, 
#     Xcode → Preferences → Downloads → Components → 
#     "Install" button to the right of "Command Line Tools".
###################

# note the archflags
export ARCHFLAGS="-arch x86_64"

# Install homebrew
ruby -e "$(curl -fsSkL raw.github.com/mxcl/homebrew/go)"

# Install git (osx provided isn't particularly current)
brew install git

# Modify path to make sure we are pointing at homebrew apps not defaults
export PATH="/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:$PATH"

# Check if brew is good to go
brew doctor

read -p "If brew doctor looks good, press [Enter] key to continue..."

# handy utilities, and a simple brew test
brew install wget

# python
brew install python --with-brewed-openssl

# handy python modules
pip install virtualenv
pip install numpy

# node, node modules
brew install node
npm install -g topojson

ECHO "Download ESRI file geodatabase API"
ECHO "Current version (Sept 2013) is 1.3, but it doesn't currently work with gdal."
ECHO "***Use version 1.2 instead***"
ECHO "http://www.esri.com/apps/products/download/"
read -p "Once file geodatabase api zip file downloaded, press [Enter] key to continue..."

# Copy fgdb api stuff to /usr/local
cd /tmp
unzip ~/Downloads/FileGDB_API_1_3-64.zip
cp -R /tmp/FileGDB_API/include/* /usr/local/include/
cp -R /tmp/FileGDB_API/lib/* /usr/local/lib/

# install gdal, with unsupported for fgdb api driver support
# note that the --complete install option bails on an xml parser xerces-c
# needed for GML (not exactly a pressing need). 
# Therefore, just do the basic install. (load pg later)
cd
brew install gdal --enable-unsupported

# presuming gdal installed successfully, load shapely, fiona, tilestache
pip install shapely
pip install fiona
pip install tilestache

# time to install the database
brew install postgresql
initdb /usr/local/var/postgres/9.2/main -E utf8 -U postgres -W

# add these to bash_profile for easy db start/stop
cat <<EOF >> $HOME/.bash_profile
alias start_pg='pg_ctl -D /usr/local/var/postgres/9.2/main start -l /usr/local/var/postgres/9.2/main/server.log'
alias stop_pg='pg_ctl -D /usr/local/var/postgres/9.2/main stop -s -m fast'
EOF
source $HOME/.bash_profile

# install postgis
brew install postgis

# start server and setup a default postgis enabled db with user postgres/postgres
start_pg
createdb postgis -U postgres
psql -d postgis -U postgres -c "CREATE EXTENSION postgis;"