Here's a link to a quick comparison of different monitor options.
http://www.oscarcontrols.com/monitors.shtmlAll things considered I think a TV is your best bet. The picture is very close to a true arcade monitor, without having to hack or use advance mame. It's also the least expensive option. People tend to feel that PC monitors display the lines too crisply and sharp to be authentic. They are also comparitively VERY expensive (compare a 27" TV price with a 27" PC monitor price).
As far as mounting goes just put the TV on a shelf and put a bezel around the screen and cover it all with a sheet of lexan, plexi or glass (preferrably smoked). The shelf is covered and as far as anyone can tell by looking at it, it may as well be a properly mounted arcade monitor.
All things considered except cost moves the Wells Gardner D9200 up to the top of the list. It's like a best of both worlds Arcade Monitor/PC Monitor. It hooks directly to any videocard and will display resolutions up to 800x600 (as opposed to a maximum 640x480 for a TV) but displays a much more "arcade-like" picture than a regular PC monitor. A new one will set you back about $500 shipped, though. It is 27", by the way.
The general concesus, though some disagree, is that a PC monitor is the least attractive of the different available options, but if you plan to use your machine for windows related tasks such as word processing, etc. a PC monitor is really your only choice. It's really very dependant on your personal situation, preference, disposable income, electronics capability (for hacking arcade monitor cables).
Keep an eye on the monitor forum. This stuff really has been discussed
a lot and you'll be able to find more info there on the subject than you could ever want. Use the search feature near the top of the page to search the forum for things like "which monitor" or "PC monitor v. TV". When you find a post that seems relevant click on the subject line of the post and it will take you to the entire thread.
Good luck.