Woops, I didn't mean a standard kvm switch. I've seen some that work the same way but allow you to select between two different monitor/keyboard/mouse/speaker setups. I'm not sure what they're called though now that i think of it.
EDIT: something like this would work.
Newegg.com - IOGEAR 2-Port VGA Video Splitter GVS62 VGA Interface Don't use the passive vga splitter that's just a cable with two female plugs. Those never seem to work as intended. It causes all kinds of issues with monitor detection. You'll probably still have issues if the monitors are a different resolution though. Using two separate ports on the video card is definitely the best way to go if possible.