I would recommend, for a beginner, softer music to start with. His entire amount of works are difficult to comprehend at first. I would hold off on most of the cantatas, but to begin with, I would start with:
BWV 82 (John Eliot Gardiner and Peter Harvey have the BESt recording out there)
Once you get familiar with the Brandenburgs, move on to good renditions of the Keyboard Concerti, and the Goldberg Variations (Pierre Hantai).
Also look for the violin/keyboard sonatas BWV 1017, 1018, and 1024. 1024 is my favorite. FAVORITE.
Source: I am a huge fan of Bach