Ranma Fanfiction:
Relentless An excelent horror/adventure fic. Happosai draws the wrath of an spirit of vengeance, but he manages goading it in chasing Ranma. Pairings are Ranma/Akane and Ryoga/Ukyo.
The More Things Change and its sequel
The Pursuit of Happiness . Ranma chosses Akane, permanently upsetting the balance of power and love poligons in Nerima. Unknowingly, Ryoga gets burdened with the responsibility of luring and unleash chaos in Nerima, meeting he has inherited all troubles Ranma had. Oh, and he isn't falling in with Ukyo. Not at all.
It is a very funny history. Sadly, the sequel is unfinished.
Daigakusei no Ranma/Daigakusei no Ukyo. Ranma and Akane are finally forced to get married and learn to get along well as they attend college. It is a continuation fic, very funny. However it is written in script format, and it is unfinished.
Girl Days. Nodoka decides she isn't worried about her son's manhood... but "his" womanhood needs training. Incredibly hilarious and loony.
Sadly, it is also unfinished.
Ranma: Hearts of Ice. Despaired and hopeless, Cologne and Shampoo try sending Akane away to the Kami Plane, where all Japanese deities live, in order to get rid of her. A multi-chapter, epic tale of love, adventure, myth and betrayal. And it is FINISHED! Hooray!
I'll Met by Starlight. This fic is enough drak and must be read with caution. What if something went awfully wrong when Genma was training Ranma, and instead of becoming a somewhat rude and jerkish but nice guy, Ranma became the bad guy?
Pokemon:
Pokemon Master. The first dark Pokemon fic, and one of the best Pokemon fics. Ten years in the future, the Pokemon world has completely changed. Team Rocket unsealed a forbidden power in order to take over the world, and in the process they nearly wrecked the world. Humans have gained elemental powers and the Pokemon League, led by Gary Oak, tyranically rules over Kanto. Only a handful of rebels oppose to its power, but they are being defeated. Misty set to find Ash and force him to join the Rebellion in order to save the world. Together, they must deal with elemental powers, forbidden pokemon... and the rekindling of their relationship.
Beautifully written, full with mysteries, drama, romance and action, it still stands like one of the best fanfiction I have read. And it is complete. However, the author began writing it before Pokemon Gold and Silver were released, and before the Johto seasons were aired, so the fanfiction only uses characters and pokemon of the first games and seasons of the show (pretty funny, he anticipated Nintendo, creating shadow pokemon before dark pokemon showed up in the games themselves).
BadgeQuest and the sequel
The Hidden Machine Saga. Ash decides earning every badge on the world. In the way, he must deal with Team Rocket... and a certain prophecy involving legendary pokemon and demons. A good adventure fic. Sadly, the author was going to write a third part in order to close the history properly, but it never was done.
Pokemon Destiny by Nova (you will ahve to scroll down to find it). In an alternate world where Misty never joined Ash during his travels, Giovanni sends his best soldiers to find and capture a legendary Pokemon. In reply, Professor Oak assembles a team formed by Ash, Misty, Brock, Gary and Giselle in order to stop him.
It is a good adventure fic, but it is unfinished. The address I have given is the only place where it can be read (as far as I know).
Kimagure Orange Road:
Kimagure Orange College. A sequel to the anime show. After the love triangle between them and Hikaru was ruthlessly broken up, Kyosuke and Madoka must go on with their lives, attending college. A romance fic, written like a screenplay.
Slayers:
Slayers Trilogy. This is The Best Slayers fic. Period. No other ever comes close. The shattering of a magical mirror sends Lina and her friends to an apparently routinely jaunt for a replacement. What apparently was another usual adventure quickly becomes a long, epic quest with the fate of two worlds in stake. And that is only the first part! Highly recommendable.
Zelda:
Legend of Zelda: Ocarina of Time. An Ocarina of Time novelization, and one of the best Zelda fics. Sadly, it is unfinished (and it practically gives fanservice by all shippings in that game).
Final Fantasy:
Final Fantasy VI The Novel. An excellent novelization for one of the best FF games (the best, IMO).
Evangelion:
Evangelion: The Second Try. An excellent time-travelling fic. After the Third Impact, Shinji and Asuka are forced to survive by working together, maturing and falling in love in the process. However, one day, they wake up and discover somehow they have traveled back in the time, right before the battle against the Twelveth Angel. They decide trying and preventing the end of the world this time. However, that second chance demanded a prize neither of them was willing to pay...
The One I Love is... During a test, Rei realizes her feelings for Shinji... and she realizes Shinji and Asuka are very close. And she doesn't like that. Rei starts wooing Shinji, prompting Asuka to drop her self-denial act and trying winning him over. All of sudden, Shinji finds himself forced to choose between two girls he feels strong feelings towards, and growing up as the battles for the fate of the world go on.
Shinji Just Snaps and Totally Wales on Everything. What the title says. Shinji/Asuka humor fic.
Super Robot Wars:
Super Robot Wars Omega. Fic based on the long-running video game franchise (a multi-crossover between dozens of mecha shows including Mazinger, Gundam, Evangelion, Getter Robo, Macross...). It is the Neo Space Century 298 year, and war threatens with breaking off again, restarting the cycle of violence and destruction. Several heroes must band together again in order to save the humankind.
It is a good action/drama story, but it is sadly dead.
Have you ever read Tolkien works? If you are interested, you can check this fanfiction:
The Leithian Script. A screenplay version of one of the main stories of the Middle-Earth legendarium, the tale of Beren and Luthien. A very entertaining, hilarious and moving story, with very well developed characters, and excellently fleshed out.