Two computers. Three screens - one control? I have a setup at home, where I have a laptop permanently connected to a screen, and another laptop that I take to work with me. Recently, I've started doing a lot of work using both machines at once - with the independent laptop sat underneath the major screen.

Anyway - I'm looking for software that will let the independent laptop treat the other computer like an extension of its screen (when I want it to) which can be easily disabled and will cope alright with multiple screens. Is this possible / does a solution for this exist already?

I've tried Apple Screen Share, which is cool but just doesn't quite cut it.
Teleport is a free application specifically for this purpose. It allows you to use one machine as a "host" with one pair of a mouse and keyboard, and use it to control (over your local network) other machines just by moving your cursor to another computer (similar to how multiple displays work, except this time on separate machines). It also integrates the clipboards of the macs, allowing you to copy/paste between macs.