Using another Mac as a display
Yep, there's an app for that.. (or two)


"ScreenRecycler" http://www.screenrecycler.com/ScreenRecycler.html
"AirDisplay" http://avatron.com/apps/air-display


I have used it, it works, but it's much better over an Ethernet connection instead of WiFi just be forewarned.

Also, you could use a (~$50) USB -> DVI adapter with the DisplayLink software for Mac and just add the monitor to your computer via USB, but honestly the performance is going to be about the same as AirDisplay over Ethernet (you just wouldn't have to run the other computer)

Anyway I have used both methods and found them to be very useable for mostly text-based work as a secondary screen.