YouTube member LJtutorials gives a run down on the new BeachTek DXA-SLR Pro. These audio adapters are used to adapt your higher end XLR Microphones to DSLR cameras and provide features like headphone monitoring, Phantom power, Cleaner Pre-amp, Manual Levels adjustment (during recording), and AGC disable. If you're already enjoying a workflow of separate audio recorders with the Zoom H4n, then this might not be interesting to you. [Thanks LJ]
If you want to capture best audio directly into the camera so that you don't have to sync in post, then these types of adapters are a must have. There are several different models of BeachTek and Juicedlink Preamps that offer different feature sets at a variety of prices. For instance, you don't need headphone monitoring or AGC disable with a Canon 5D Mark III, and you may not require XLR and Phantom power if you're using Self Powered Microphones. This review is based on the the DXA-SLR Pro version which will run you over $400 dollars (found here).
Beachtek DXA-SLR Pro HDSLR XLR Audio Adapter