Another one I may have shown on here before. Einhander. I have a specific color filter that does wonders for this game.
Oh and FF7. Also using the same color filter. People tend to use the default texture filter with this game but I think it always makes the game too smudgy. Instead I use the Stretched 2x mode, which is like a 50% blend.
Silent Hill. This game benefits massively from emulation. Not just from higher resolution, anti aliasing, and all that. It also removes the terrible fake fog method the game generally uses on a real PS1, where it's just a mess of dots on the screen. Also I may be wrong, but you can finally force vsync, where on a real PS1 game, the game constantly out frames tearing.
Zelda: OoT has had many active re-texturing projects, but the "realistic" one was my favorite, although it was never finished. It was by far the best looking.
You can also find some pictures taken from nullDC in this thread:
http://www.racketboy.com/forum/viewtopic.php?t=2410