The Rose Garden is THE place to go for all your Harm/Mac shipping needs.  The site has many goodies, including pictures, wavs, videos, spoilers, fan fiction, games, articles, graphics, and more!  Definitely worth the time.
 

Semper Harm & Mac is a nice site with an explanation of the 'ship, some photos, a list of the best shipper moments, creative works of the fans, and more.  I liked this site when I first found it, and I still like it.