You might like to try the following sites:
Ariana's Stories Stories by Ariana covering all four series of Star Trek, with particular emphasis on The Next Generation and Deep Space Nine..
Archives of The Lost Tomes Vulcan oriented adult fan fiction based mostly on The Original series.
The Best of Trek Fanfic Last Updated 28th August 2003
Claire Gabriel's Fan Fiction Includes a long novel about Spock's family, a sequel to that novel, and a link to three Voyager J/C stories by the same author.
Gamin Davis' Spock Treks Friendship stories of Trek's most beloved duo: Captain Kirk and First Officer Spock. Here are tales about Spock's childhood and his love interest, Christine Chapel. Also there are a host of poems and filks.
Gloria's Star Trek Fan Fiction Home Page These stories, originally published in zines, are Kirk and Spock friendship stories with some action adventure thrown in.
Invisible Planets: Jungle Kitty's Star Trek Fiction Over 100 stories (many of them award winners) set in the TOS universe. Mostly het, some gen, some slash.
Kathleen Dailey's Fan Fiction Page TOS and TNG-era fiction, with an emphasis on Romulan and Vulcan stories. Links to recommended authors and web sites of interest.
Linda C Wood's Website Site features 10 zines on Leonard Nimoy character stories and poems, UNIVERSER and UNIVERSER 2 solely Star Trek poetry and prose.
Rabble Rouser's Rec Room Fanfiction based on Star Trek: The Original Series, mostly gen, ranging from G to Adult. Also has reviews and links to other fanfic websites.
Roisin Fraser's Web Site This site contains some adult content (R-NC17) but is mostly gen, centered in the TOS Universe. This site is home to the T'Rela Series, the Intermission Series and T'Thelaih's Vulcan Oasis. Ratings are clearly posted, please read them. :O)
Sarek and Amanda's Lair This is a site for stories, pictures and links of Vulcan's favourite First Family.
TOS fiction by Nesabj This site has some excellent realtionship stories.
Wildcat's Trek Fiction A collection of het and slash stories, with an emphasis on Spock/Uhura.