Revised information as of 10 May 2011 is at end of article.
Revised information as of May 2012 listing iTead and Seeed size and quantity options is at end of article.
After you've developed a circuit, perhaps tested a prototype and have finally got the perfect design, you may wish to create a printed circuit board. There are some home-brew methods, but if you get to the point of wanting more than a few boards, it may be time to turn to a commercial fab house. Even in small quantity, having circuit boards made can be inexpensive, if you know where to go. Making circuit boards in large quantities will further lessen the price of the board - in my experience with production boards, making ten times more boards increases the price only be a factor of two! With a large order, there are always the anxious moments wondering if you missed some detail on the board, or if the fab house will do a good job.
To help you find a good fab house, the tables below list some of the sources I have used that produce good boards as a reasonable price.