KVM Switches - What you should know:

The Main Considerations are:
A) Number of Computers to be controlled
B) What Monitor Connectors They use -VGA or DVI, etc
C) The Keyboard and Mouse Connectors (PS/2, USB)
D) Other Connectors (Audio,RS232,USB 2.0, etc)
E) Matrix or Single Output?

MINI FAQ:
1) USB KVM's with PS/2 Inputs will control USB Connected Computers with PS/2 Keyboards and mice.
2) KVM Switchers can be used manually with pushbutton switches or by using "hot keys" on your computer keyboard, the hot keys are generally configurable.
3) USB keyboards and mice are compatible to varying degrees with Macs and PC's. 4) DVI Dual link KVM's will work with Single link and Dual link Computers and displays, supporting both types of resolution. Single link DVI KVM's will only support single link resolutions.

There are a couple of not so obvious things to keep in mind as well. Do you want all connectors in the back? Do you want Daisey-chaining support? Signal Extension Capability? What Resolution Video do you need? If VGA, higher resolutions require better bandwidth capability. If DVI, do you need Single Link (1920x1200 max) or Dual link for higher resolutions?
5) Connectors on KVM's are very inconsistent, some use males, others females, some use DB25 connectors which require proprietary cables. Check and recheck the specs

KVM over IP
Remote server management hardware tool to remotely control servers, either over the Internet or over your local network. Fully emulates a screen, keyboard and mouse, giving the user complete control over the attached computer. Some models include KVM Switching for control over multiple Servers.

Secure Console Servers
Allow IP connections to secured Serial port server connections for access to controlling firewalls, and other RS232 serially controlled systems remotely over the internet. All with enterprise class security.