A number of solutions depending on what exactly you want to do:
– Manage files and do general editing stuff: Aperture or Lightroom. I use Aperture, but it does have a problem with lack of support for new cameras.
– Heavy duty creative editing – Photoshop is pretty much the gold standard, not least because of the amount of training material available
– Convert RAW files – for my money CaptureOne knocks the socks off the others, but it does not have detailed editing capabilities like Photoshop.
– Nikon Capture NX2 – a compromise between Photoshop and CaptureOne
Of course there are other programmes, but these are ones I'm familiar with …