I don't think I have particularly interesting fantasies, nor are they on my mind very often, and I think they mostly come from porn.
1) I would like to have sex with a considerably older woman, a busty one.
2) I would like to have sex with a black woman.
3) I would like to participate in a male-male-female threesome, including double penetration. I'm not in the slighest bit bi, but for some reason I find FFM threesomes weird (tons of holes and one dick), and MMF more intense and erotic. I would not like to do this with my partner, though, as I would probably get a bit jealous.