Nikon has sent out quite an enticing deal for the month of May. With the purchase of a D610, D750, or D810, you can get the respective battery grip for free. This is a huge savings, as the grips for these cameras are expensive. Essentially, you're getting an extra $350 rebate on top of the already fantastic sales that Nikon has had available on their bodies.
The MB-D16 for the D750 normally costs $350. That's a good chunk of change towards a lens, flash, or bag. This deal is going through the rest of the month. Battery grips afford you a few things: comfort, extended battery life, and easy vertical shooting. For long days of handheld shooting or working with longer lenses, a grip can make a lot of difference in your comfort level. For free, that's a big deal. While there are a variety of off-brand grips available on the market, I've found that the name-brand grips tend to be more solid (best construction), have better contact with the body (less wiggle during long exposures), and better ergonomics. For those of you that, like me, prefer the size and feel of pro bodies (D5 or 1D X Mark II), this will give you exactly that. Be sure to take advantage of this deal by picking up a D610, D750, or D810!