They're called KVM switches (keyboard-video-mouse) and allow you to run 2 (or more) computers through a single station; they're fairly cheap, and come in a million different flavors. You can get one with just a monitor A/B switch if that's all you really need. I know Black Box corp makes quite a few, but if you look around, you can find a slew more.
Monitors with two (or more?) inputs can also be used on two computers.
My Iiyama Visionmaster Pro 410 has both a VGA 15-pin and a BNC-5 input, and I have one computer hooked to each. You can switch between the two via the menu, and some monitors even come with a quick switch key.
I have two sets of keyboards and mice. They're not as hard to tuck away as you might think.
The advantage here is you don't get the distortion normally seen in cheap KVM switches, and you'll pay near or over $100 for a high-quality video switch. My friend's $30 KVM switch has terrible ghosting problems. Might as well spend $3-400 for no distortion and get a new monitor out of the deal.
This signature space FOR SALE
[This message has been edited by MadCat (edited 03-29-2001).]
My Mitsubishi Diamond Pro 900u not only has dual video inputs (VGA and BNC). It also has a built-in USB hub with dual inputs that are slaved to the video input. I tried using it as a KVM switch with a USB mouse, but one of my boxes has an old MB that doesn't handle hot-switched USB devices very well. And USB keyboards don't work in the BIOS, which makes them quite useless.