My family's Christmas present was a Nikon SB-800 Speedlight (flash) for my D70. I'd previously been shooting using a decade-old SB-28, which I rarely used due to the awkwardness of getting a satisfactory exposure (it's not 100% compatible with the D70.)
Not only is exposure great on the SB800, but it comes with a filter to tune its light color temperature to the same as tungsten bulbs, which helps eliminate that funny blue color cast that we all associate with flash photos. I used to do this with Roscoe lighting gels, but it's really even better when combined with perfect flash exposure.
Now that most SLRs come with a built-in flash, the external flash unit is a less common sight. But if you spend hundreds on lenses, you might want to consider dropping the dough on an external flash -- it really does make a huge difference when set up properly.
Coming soon: 2005 photography New Year's resolutions.
