X2X.

If you've never heard of it, you're missing out.

Two or more machines, each with their own desktops, but one keyboard and one mouse.

When you move the cursor out the right of your first desktop, it appears at the left hand side of your next desktop - and so on and so on.

It turns as many desktops as you want into one virtual one.

Did I mention it rocks?

If you've got a Windows machine, there's also X2VNC.

and if you're using unix+mac, there's also synergy.

If you're on Windows there's also MaxiVista

thats all three, but only for mouse/keyboard.