Monica's Mercato (of the Monica's empire) is my favorite place for salumi (all the cured meats: salamis and other sausages, prosciutto, etc). The people there are very knowledgeable about their stock, and they know which things are seasonal and what is always in stock.  This is where I get the cotecchino for the holidays, and they have Porchetta, too!

It's a cluttered shop. Once you get in the door (no sure thing) there is very little room to move around, so it's a good idea to have a good idea what you're after before you go in if they are busy. Of course, that's because they have so much great stock, it's just sometimes tricky getting a chance to explore it.