Comics artist and Loaded Blanks publisher Ezra Claytan Daniels has generously offered up this link to the Pitch Packet he talked about during his class visit last week. Not sure what a cover letter should look like? Wondering about the difference between a synopsis and a preview? He's laid out his own examples here, which you can use as a model to put together your own comics pitch for publishers. Just don't try to plagiarize -- publishers will recognize straightaway if you've copied parts of someone else's ideas or phrasing.
On another note, here's a brilliant packaging idea from the publisher of Parfait, the hand-bound zine/artist book edition by Brooklyn-based Emily Larned. Sell one version of your publication for cheap, and another with some handmade, limited-edition freebie attached (in this case an "electric animal" in customized packaging) and charge a little more. This also works for covers - you can make a cheapie version with xerox only, and a limited-edition run with silkscreened covers. That way everyone gets to enjoy the content, and those willing to pay a little extra for your time can appreciate it as an art object.