Well, there is no actual emulator that can run games 100% perfectly. Some may come really close but they're always off by a little. Anyways, I found Connectix VGS to be the most accurate PSX emulator available. It most faithfully emulates the games and if played on a TV with s-video it looks exactly like the real thing. It's missing some sounds though and it can't run all games (although it has by far the highest compatibility, especially with the games.txt and patches).