5-Pin DIN (AT): It was used in older AT PC as their motherboards come with these keyboard connectors. They are not hot plugging.
PS/2: ATX motherboards come with PS/2 keyboard connectors. They are hot plugging.
USB: They are hot-pluggable and some have USB connectors, to connect more USB devices.
Wireless: These come in the USB and PS/2 varieties and can use infrared or Bluetooth.