A good question. I do most of my shopping at Sky High Comics (172 South Rancho Santa Fe Rd., San Marcos), at Southern California Comics (8280 Clairemont Mesa Blvd. #124, San Diego), at Comickaze (5517 A/B Clairemont Mesa Blvd., San Diego), at the annual San Diego Comic Con (a great place to find out more about comics), and online at some of the following sites:
Many of the books mentioned on these pages are available from the Palomar Library, which has a first-rate collection of graphic novels and secondary sources about comics. Click here to see the ever-growing list of comic books in the Palomar College Library. Also, the UCSD library has a good collection.