Want to get the best from your Nikon DSLR NEF files? Capture NX does the best job of processing Nikon's proprietary NEF format RAW files. If you are using a modern Nikon lens with your camera it will automatically remove chromatic abberations and vignetting.
I use this with my D200, and it does a better job than any other RAW convertor I've tried. It also has 'U-point' technology, which is quite a clever way of applying adjustments to only one part of the image.
While it will work with TIFF/JPEG files from non Nikon cameras, I wouldn't bother buying it if you don't have a Nikon DSLR. Also it doesn't include patch/clone tools like you get in Photoshop. I think NX2 has these, but that's a lot more expensive.
This software normally retails for £120, however a new version has just been released, so this version seems to be discounted. It is available for this price at Park Cameras and Warehouse Express. Also available from Bristol Cameras for £1 cheaper, but their rating on froogle isn't very good.