Beautiful 1080p video deserves better sound than what any DSLR's internal microphone can offer.
If you're looking for some audio firepower to accompany that new D5100 DSLR, Nikon hopes you'll consider their DSLR-specific ME-1 stereo microphone. It attaches via the camera's hot shoe and uses a standard 3.5mm stereo jack so it'll work with any of Nikon's other HD-video capable DSLRs -- or any other camera with the proper jack for that matter. It draws its power from the camera's battery, so there's no extra pack to carry around.