dslr

tl;dr: You can (and should) pick up one of these things if you have a D90 or D80, and shoot vertically or need extra juice for the camera. The Nikon MB-D80/OEM model is a bit more solid, but you can't beat the Phottix's price!

Take a look at what's hanging on the neck of almost any professional photojournalist, wedding photographer, or camera guy—you'll almost always see the tank-like and bulky body of a Nikon D1/2/3/X-series or Canon 1D-series SLR. The Phottix MB-D80 takes your D90 (in my case—it also works on the D80, though) and gives it three of the tank-like bodies' functions:

1. A vertical shutter release/controls: When shooting portraits, this is immensely helpful.
2. Double the battery life: You can stick an extra Nikon EN-EL3e battery in the grip (bringing your total to 2 batt's!).
3. Look like a serious photographer: 'Nuff said.

The battery grip performs great, it can take a beating, and the shutter release and controls feel almost as good as using the controls on the camera body itself!

tl;dr: The Nikon D90 DSLR is one of the best 'prosumer' digital SLRs produced in 2009. It's low-light performance is exception for the price, and it can work well as a backup body to a camera three times as expensive. The HD video mode, a first for digital SLRs, is half-baked at best.

(Above: The D90 with my favorite walk-around lens, the AF-S 18-70mm f/3.5-4.5).