Launch iTunes and iPhoto when external USB drive is connected
You can do that very easily using ControlPlane, a free (open-source) application:


  ControlPlane, a fork of MarcoPolo, brings context and location sensitive awareness to OS X. With ControlPlane you can intelligently reconfigure your Mac or perform any number of actions based on input from a wide variety of evidence sources [...]


from: https://github.com/dustinrue/ControlPlane

It's very easy to set-up. You define a "context", select a rule (or multiple rules):



And link an action to it: