In PS CS I used Digital Film Tools' plugin called
55mm. It has since then been sold and maintained by
Tiffen (read, now cost nearly 3x the original amount), but it is a comprehensive bundle of filters for photographers.
Also, most plugins available from
Nik are excellent.
Earlier times I heard a lot of people using Noise Ninja.
You weren't clear on what you're attempting to accomplish, but if you're trying to simply have better control over your digital negatives and you're missing some of that control that you once had in a darkroom (if you've ever been) then the 55mm set is amazing.