There's been quite a bit of discussion in the past on this forum about NegPos, David Dunthorn's Photoshop plug-in for accurate handling of scanned colour negatives (and b&w).
David has now released a next-generation product called ColorNeg. You can find it here: http://www.c-f-systems.com/Plug-ins.html. As a committed NegPos user, I've only spent an hour or so playing with it, but if anything, I would say it gives even better colour conversions than NegPos did. The user interface is simplified, while keeping all the advanced functions still within reach.
If you are a registered NegPos user, ColorNeg will share your existing licence key. If you are not a NegPos user, and you shoot colour negative film, now might be a good time to check it out.