Anything, so long as it's mutually enjoyed & takes fewer than 3 days to physically recover from {ie no sprains, broken bones, transmitted std's}
Experience has taught me that I tend to most frequently want sex:

• When I first wake up in the morning, or at least before I've involved myself in any of the day's projects
• In the evening if I've been spending time during the day being attracted to & interacting with the person with whom I'd be having sex
• Most of the rest of the time, if the interest is mutual

Experience has also taught me that I tend not to want sex:

• Anytime I have the impression that the interest isn't immediately mutual
• After eating a large meal (But I seldom object to eating a meal after sex.)
• While I'm processing unpleasant emotional confrontation
• If I feel like I'm not clean, especially if I've felt that way for a while

A few of the less mainstream sexual practices I've encountered on the internet sparked an interest. They include:

• Tantra Yoga
• M/F Spanking
• Some Bondage (especially those artistic looking photos from Japan & some involving hot wax)

The bulk of my interest is (& all of my experience has been), however, fairly prosaic (or so it seems to me).

Note:
I consider sex to be a social activity, so my aforementioned uncomfortableness with interacting in large groups of strangers applies here.