The Nikon D800, despite not being one of Nikon's single-digit flagships, is currently the highest-resolution 35mm digital SLR on the market with its 36MP CMOS sensor. An almost identical model, the D800E, differs only in the absence of a functional low-pass filter to increase resolution at the cost of increases of moire.
The obvious competitor for the D800 is Canon's EOS 5D Mark III, both of which are excellent full-frame cameras for studio and portraiture where the moderate burst shooting advantage of the EOS 5D Mark III is less important. The D800 provides higher resolution and dynamic range which would give it a an advantage if someone were looking to choose which system to purchase.