One of the recent issues of Shutterbug magazine did a review of RAW processors and found that most did a comparable job on the processing. If you are looking to process 100's of shots at a time, some have better preview, file selection, thumbnail generation, etc.
I don't shoot with Nikon, but I like Photoshop - good integrated RAW processing, file handling, etc. Adobe Camera Raw (ACR) is a plugin they provide that supports most RAW camera formats. This gets updated every 6 months or so for new cameras.
Pixmantec released a free RAW processor called Raw Shooter Essentials sometime back.
http://www.pixmantec.com/
They did this as a freebie, indicating they would release a pay-for pro version, which they did a couple of months ago. The freebie version has a limited feature set, I've used it and it's OK.