I guess I'll start, and instead of starting with a story I'll start with a whole series. You can reach the author profile at:
www.fanfiction.net/~notmanos. The first story of the series is at the bottom, and is called "Non Zero Possibility," reached directly at this link:
http://www.fanfiction.net/s/1129340/1/Non_Zero_Possibility
Okay, this is going to sound slightly more than slightly strange, but trust me on this when I say right now that this series is probably the best bunch of fanfiction stories that I've run into out there.
Category: X-Men movies x-over with Angel tv show with a heavy focus on Wolverine (starts after the first movie, and during the second season respectively. And btw, having a big knowledge of Angel, or even liking him at all, is not a requirement. I had no idea who he was when I started reading this. As the series progresses, it takes into account and accommodates for X2 and X3).
Main characters: Wolverine, with Angel, the X-Men, and hilariously original, well-rounded, and . . . interesting OTs appearing every few stories.
Rating: M/R for suggestive material, plenty of violence (it's Wolverine, need we say more?), and very excessive bad language. If you are bothered by the use of the f bomb and every other curse in the book, be warned. I just paste it into Microsoft Word and use the "replace" button.
Length: This series is gloriously long, with probably 50 stand-alone stories ranging from 30,000 words to 70,000 words. Yeah, freakin' long, but still too short.
Reasoning:
This is a weird bunch of stories, but I love them to death, and they're surprisingly well-written (better than a whole lot of published authors, especially after the first story when notmanos really hits his stride). The author is original and quirky, and has a gritty writing style that is realistic (which is surprising considering how insane the plotlines sometimes run), stunningly powerful, and yet hilariously sarcastic and packed with original dry wit. It's also crammed-full of trivia, background information, and cultural references that often leaves me wondering how in the world a single author thinks of these things, let alone puts them together so well.
I'm a long-time Wolverine fan, and this author has caught the spirit of Wolverine--taking what they have in the movies and drawing it right into the full-rounded character that I love. Throughout the stories there are a number of run-ins with Weapon X, other mutants, and crazy vampires and other demon-craziness (which actually works better than you would expect). Since it starts in movie-verse, Wolverine is searching for answers for his past, and before the end we get plenty of glimpses and flashbacks into a number of wars, his history as a samurai, and an adaption of the Mariko story (which is completely amazing).
notmanos even manages to take the Phoenix Fiasco from X3 and make it less than lame.
Highly recommended. I passed it up more than a few times because I was dubious about the supernatural element, but I'm glad I eventually got bored enough to overlook that and give it a try.
If you like it, drop him a review to encourage him to speed up with his latest.