My ab has a 19" LCD monitor, which is what it came with when I originally bought it (pre-made cab).
It's a Dell TN panel mounted vertically, and the viewing angle off to the left is pretty poor. Looks fine when you're right in front of it or off to the right, so the machine is actually right next to a wall to prevent you moving too far over

But with the HLSL shader effects emulating a CRT it looks pretty good.
I've got a replacement monitor lined up for when I eventually get around to replacing it, which is a 20" HP IPS monitor. Trouble is it's bigger than the old one, so it's not a direct replacement. I'm reluctant to pull something apart if it's working well enough in normal use.
When going for LCDs the best panels are probably IPS because of the viewing angle, availability and price. The problem is it's getting almost impossible to get 5:4 or 4:3 IPS monitors (at least at a reasonable price), so you may end up having to use a wide-screen monitor and blanking off the extra bits if you want an original arcade aspect ratio.