One cinema display with two macs
At work, we refer to such devices as "switch boxes," though it appears that "video switch mini displayport" pulls up what you're looking for. The following appears to be what you're looking for:

4-port DualView Mini DisplayPort KVMP Switch with Peripheral Sharing

Of course, you're just interested in sharing the display, but it does have a built-in USB hub, in case that's needed. It has a good desktop footprint, as well.