I have a large number of doujinshi for sale here and here. (sorry for the separate posts, it was too much to fit all in one)
The first link leads to manga-related doujinshi, mostly Naruto and Samurai Deeper Kyo, but there's some Bleach and Digimon as well. There's yaoi, het, gen, pretty much something for everyone.
The second link goes to "western" fandom doujinshi, namely Harry Potter and Lord of the Rings. This one includes some rare gems such as Shisinden books.
Detailed descriptions and several sample scans are included for each doujinshi.
Feel free to take a look. Thank you!