Nifty is one of the oldest online sex story sites around. Established 1992, and featuring over 235,000 stories by over 15,000 authors, Nifty has a great collection of LGBT sex stories.
EscapismCentral is a very popular site that promotes lesbian sex stories. The site hosts both user submitted hardcore fiction, as well as features links that promote published authors.
Gay-Story.com is one of the top small to mid-sized LGBT sex stories sites, and features a tremendous collection of gay sex stories
LushStories.com has an enormous membership, so even though you don't need to sign up to read the stories, you will want to be part of the crowd.
EroticStories.com is a very impressive collection of LGBT sex stories, which includes gay, lesbian, bisexual, and transgender as separate searches. There's even a straight section but who cares?
TG-Fiction.com is a medium-sized collection of Transgender sex stories (both fiction and non-fiction) that is one of the most well designed sites in the genre.
HarperBliss.com is a best-selling author of lesbian romance novels, and this is her personal site, which is full of samples of her lesbian sex stories and lots more.
LesbianStories.com is a premium sex story site for lesbians with a huge collection of steamy tales of women who love other women.
GayAuthors is a site full of gay stories (both sex stories and not). 1,146 Authors, and 4,585 Stories at present.
Blithe.com isn't exclusively LGBT sex stories, but rather a website that promotes lesbian, gay, bisexual and transgender writers.