A lot of confusion surrounds printers, publishers and distributors. You know that both printers and publishers make books, so aren't they synonymous? Not at all.
A printer prints books (and smaller ones will also print stationery!). Simple as that. They must be paid to print books. They don't promote them or distribute them. The most they will do is mail the books to their final destination, be it your home or a distributor's warehouse. Some small press printers might keep some copies of a book on consignment to sell as novelty items or to showcase their work, but most of the times, a printer just takes your money and gives you books. They will print books for individuals, groups and even publishers. They do not publish books. They only print them.
Publishers usually don't print books themselves. They use printers! See, a publisher is to comics what a producer is to movies. They front the money and handle all the loose ends. They publicize their books and add them to a catalog which gets sent to distributors. They brand books with their publishing house name (like "Marvel Comics"). Really big publishers, like Random House, quite often have in-house printing. That is, they don't pay an independent printer to do the job. They own their own printer. This way if the printer doesn't return their emails, they fire him and hire someone who will :) It would be nice if we all could own our own printer, but only the biggest of publishers can afford it. Those big publishers also usually have their own distribution services, but more and more publishers are handing distribution over to independent distributors these days. Why? Because it makes it easier for them to focus on which books they should pay to have printed and how they can advertise and promote those titles.
Distributors amass warehouses of books and use them to build a great big catalog which they send to book stores. The book stores then buy the books from the distributors. Most bookstores want to be able to send books that didn't sell back to the distributor whence they came for a return on their investment. Hence, distributors can be some of the most difficult people to sell a book to if you are an independent publisher. You don't have big publishing house endorsing your work. How can they be sure Barnes and Noble isn't going to send every book back because you didn't bother to advertise? Distributors also take a rather large chunk of the cover price for themselves as payment for their services, so working with a distributor is expensive. Usually it is necessary, though, because book stores don't like having to track down individual publishers to order from. It is easier for them to simply open a catalog and place a large order with one company rather than with numerous publishers.
These three entities work together to bring both books and comics to the stores where you buy them. A self-publisher will have trouble trying to find a printer that does good quality work and a distributor willing to take a chance on an independently produced book. The comic world suffers from a lack of both printers and distributors who are capable of working with independent creators (i.e. creators who have not signed on with a publisher, major or otherwise).
Diamond Comic Book Distributors is the major distributon channel in the comics business. They are the distributors that Barnes and Noble and Walden Books and other book stores like buy from. There are smaller comics distributors like Cold Cut, but they do not have relations with book stores because book stores are, well, not exactly with the times. So, Diamond has a monopoly over which comics actually make it book store shelves. Pretty sucky with their new "all new comic titles must earn $600 in pre-orders or we won't carry them or fulfill any orders placed for them" policy. I have heard you can appeal to traditional book distributors like Baker & Taylor, though.
As for printers, well, I have had really good experience printing mini comics with South Island Print Services.
If you know of any good printers or distributors who cater to small press, leave their name and site in a comment.