Checkout and launch SABnzbd+, CouchPotato and SickBeard on startup. Put the launchagent plist files in ~/Library/LaunchAgents

_mediacenter_setup.sh

# you'll need homebrew too

cd Sites

git clone git://github.com/midgetspy/Sick-Beard.git sickbeard
# Probably need this:
# sudo easy_install cheetah
#
# test:
# python sickbeard/SickBeard.py

git clone git://github.com/RuudBurger/CouchPotato.git couchpotato
# ...
# python couchpotato/CouchPotato.py

git clone git://github.com/sabnzbd/sabnzbd.git sabnzbd
# TODO you need to configure sabnzbd once using your browser... 
# python sabnzbd/SABnzbd.py

# Then copy *.plist files into ~/Library/LaunchAgents/
# make sure to kill any test launches from above

# Setup all 3 to run on launch, and restart if crashed
# lunchy gem provides an easy interface to launchctl
gem install lunchy
lunchy start -w sickbeard
lunchy start -w couchpotato
lunchy start -w sabnzbd
# lunchy start -w sickbeard

com.couchpotatoapp.couchpotato.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.couchpotatoapp.couchpotato</string>
  <key>ProgramArguments</key>
  <array>
       <string>/usr/bin/python</string>
       <string>/Users/jamie/Sites/couchpotato/CouchPotato.py</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
  <key>KeepAlive</key>
  <true/>
  <key>WorkingDirectory</key>
  <string>/Users/jamie/Sites/couchpotato/</string>
  <key>ServiceDescription</key>
  <string>CouchPotato</string>
  <key>UserName</key>
  <string>jamie</string>
</dict>
</plist>

com.sickbeard.sickbeard.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.sickbeard.sickbeard</string>
  <key>ProgramArguments</key>
  <array>
       <string>/usr/bin/python</string>
       <string>/Users/jamie/Sites/sickbeard/SickBeard.py</string>
       <string>--quiet</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
  <key>KeepAlive</key>
  <true/>
  <key>UserName</key>
  <string>jamie</string>
</dict>
</plist>

org.sabnzbd.sabnzbd.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>org.sabnzbd.sabnzbd</string>
  <key>ProgramArguments</key>
  <array>
       <string>/usr/bin/python</string>
       <string>/Users/jamie/Sites/sabnzbd/SABnzbd.py</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
  <key>KeepAlive</key>
  <true/>
  <key>WorkingDirectory</key>
  <string>/Users/jamie/Sites/sabnzbd</string>
  <key>ServiceDescription</key>
  <string>SABnzbd</string>
  <key>UserName</key>
  <string>jamie</string>
</dict>
</plist>