It's a pretty standard Rails hipster setup on a Mac using TextMate as the editor.

I'm using a 27" Dell U2711 display.

The left hand Terminal is used for monitoring autotest (an automatic test suite runner for Ruby/Rails) and messing around with the interactive Ruby shell (IRB), git, etc.

The right hand Terminal is used for monitoring requests as they come into the development environment's web server.

The Windows XP Professional is running on VMware Fusion and used for IE testing. I use Visual Web Developer 2008 for debugging in IE.

I've got two Chrome windows, one for API documentation and one for testing, with a permanent Developer Tools window at the bottom right hand corner of the screen.