Haelga, in Riften. Her associated quest, as well as items found in her bedroom, are quite sixual.
I believe it's Brynjolf who tells you that his Falmer Blood Elixir allows you to 'make love like a sabrecat'.
While not technically sixual, Mikael the bard wrote 'A gentlemans guide to Whiterun', which basically describes the women of Whiterun as potential love interests.
Honestly, I'm glad that Skyrim isn't full of sixual content. It'd ruin the game for me - I play Skyrim because I want an RPG, not an advlt film.
