With most standard videocards you can use a solution like
Soft15khz or
Powerstrip both of which will convert your video signals to work with a conventional arcade monitor or TV.
Alternatively you can use an
ArcadeVGA graphics card from Ultimarc. This comes in both AGP and PCI-E variants and is based on the Radeon 9250 or Radeon HD2400 range respectively.
It has to be said though, you can achieve very satisfactory results using a PC CRT by enabling things like Bilinear filtering and using the in-built scanline filters that come with most emulators.
The only real necessity for using something like an ArcadeVGA is if you are running Mame on an Arcade monitor where the resolutions flip from game to game and use lots of very non-standard resolutions.
Hope that helps.