Wingless - if you haven't done it at least once, why not just talk with her about it and try it. Maybe she'll enjoy it from you more than other times.
As for myself, I dunno. There are plenty of things I wouldn't mind doing, but nothing I think of recurrently enough to call a fantasy.
If I had to name just a couple things, I'd, first of all, have to go cliche and say a FFM threesome. One day I'll find a willing second girl and get onodrim to go along as well
I don't even care if they focus more on each other than me! As for other things, definitely would like another cliche - sex on a beach.
Of course, now that I think about it, almost all fantasies are pretty cliched. Probably from everyone having the same basic desires.