Arcade monitors give you the true look of arcade graphics that you cannot get using a TV or a PC monitor. Original arcade games ran at lower resolutions than both pc and TVs can run, which accounts for the difference in authenticity when comparing arcade monitors to other displays. Arcade monitors are the obvious choice for those looking for the absolute closest to "the real thing" in a MAME machine.
There are two broad types of arcade monitors that are used fairly often in MAME machines: "Original" 15khz monitors or Multisync monitors that will display 15khz signals, medium resolution signals, as well as PC resolutions. Betson and Wells-Gardner D9200 arcade monitors work great with a PC as you are able to use them at standard PC resolutions (usually 640x480 or 800x600), and they connect using standard VGA connections. These monitors will then change resolutions during gameplay to display the correct game resolutions. You can also use standard Arcade monitors but you will have to wire them up in order to be able to connect them to your PC using a hacked VGA cable.