The following are some of my favorite Diablo fanfics . They are only a chapter or two each, for the complete stories, follow the links provided.
Hell Craft by Steven Dong
ValHallas Journey by Steven Dong
The Unholy Grail by Dalai Lama
Of Destruction and Hate by Loren Sandboe(full story will be listed soon)
Tales of the White Wolf by Rikor (link coming soon)
Other fine stories may be found at: Swift's Diablo Lair