For fans seeking images of their favorite anime, there are many sources to choose from. Fans can buy anime posters, playing cards, pencil boards, original cels, image CD-ROMS, T-shirts, etc. -- whatever form is most pleasing to them. Fans can get images off the internet as well, but for people who want lots of high-quality images, packaged nicely and affordably, artbooks are often the way to go. A large percentage of images found on the internet are scanned from artbooks in the first place, and any given artbook is likely to have many images in it that cannot be found on the Net.
In an artbook, one will usually find (depending on the specific book) original illustrations, paintings, design sketches, line art, poster art, production details, seiyuu info, staff interviews, manga short subjects, and a fold-out poster or two. As such, artbooks are an excellent package of information for the discriminating image consumer. Anime fans who are also book enthusiasts take naturally to collecting artbooks, as they appreciate the finer pleasures of physically holding and flipping through a well-designed book. Artbooks are not as good as posters in terms of decorative value, but they have a greater effective image-to-volume ratio (you need a lot of wall space for posters, whereas an artbook with lots of images is just fine sitting on your desk) and are easier to maintain.
Outside of Japan, one can find artbooks for sale on the internet, but it is generally advisable to browse through a book before buying it to see if it's actually what you want. Since I don't read Japanese, I don't buy artbooks for their text. Instead, I look for the ones with the most pretty pictures, preferably in color. Black-and-white design sketches and line art are nice, but those exact same sketches often appear in magazines such as Newtype and Animage.
I generally buy my artbooks at anime conventions. Usually, convention dealers will have most of their books on open display, unwrapped, and easy to thumb through. One can also find artbooks at large Japanese bookstores such as Asahiya and Kinokuniya. The selection is often limited, but if you know the ISBN for the book you're looking for, they can special order it for you. The main problem with Asahiya and Kinokuniya is that the books are often wrapped in plastic, so you can't look through them. They aren't usually wrapped at the top, however; with a little practice, you can get quite good at determining the contents of an artbook by thumbing across the unwrapped top portion of the book and peering in to see if there are color images or not. If you're on a New York City trip, stop at Asahiya, Kinokuniya, and the Virgin Megastore if you're looking for artbooks.
Artbooks make an excellent addition to any anime collection. If you're a fan of any particular series, artist, or studio, there are many artbooks out there that you are likely to enjoy.
[12/2/04 Update: For further articles by Lawrence Eng, see his anime page.]