As I get back into development I am struck by a simple truth - two monitors makes you a much more productive developer than one. On the basis of that I have unhooked my monitor from my games machine and stuck it in the back of my notebook (which is spec'd well enough to be a decent dev machine).
But - then I accidentally came across this http://www.maxivista.com/. It allows giant desktops to be created over wireless or wired. The slight wart - if you have a primary machine running Vista you need to use a legacy display driver which is a no go for me... nevertheless, very cool!
In their own words:
The MaxiVista Pro Edition can even link up to four PCs to create a giant desktop space of up to 7,680x1,600 pixels: