Manga is simply the Japanese version of comic books or graphic novels. Many anime series are based on a manga series.
Any anime fan would love the original manga their favorite anime is based on.
For original Japanese manga, you can usually find some on eBay and at Japanese importers like JustManga and Manga.com.
For the most popular anime series, like Inuyasha, you can find English translated manga books at many major bookstores.