D-Link 4-Port USB KVM Switch (DKVM-4U)
This is a pretty simple switch that offers USB and VGA connections for four systems, so be sure that will work with your mouse, keyboard, and monitor as well as the ports on your computers. Two of the connectors are on one side with the rest on the other; this is a bit strange design-wise but not detrimental to use. You can switch devices by pressing buttons on the device or through keyboard shortcuts, though the buttons are quite a bit smaller than they really should be. The overall look and feel of this switch is just not as refined as some of the other best options on the market, though it's still an excellent choice. While two sets of KVM cables are included, you'll need to get more cables if you plan on using this switch with additional systems.