- L-arginine
L-citralline
Yohimbine
Dopa Mucuna
Horny Goat Weed
EDIT: Weed itself (now how could I forget that one!?)
Longjack (aka Tongkat Ali as mentioned by DTWarren42 below)
Korean Ginseng
Ginkgo
Fenugreek
Boron (boosts free testosterone further even if your testosterone is good)
Beet root extract
Maca Powder
EDIT: DHEA
EDIT: L-Carnitine
EDIT: Extra strength garlic oil (per SteamFitter below)
The ones I think are more for imminent sex are: L-arginine, Horny Goat Weed, Dopa Mucuna, Yohimbine. But I haven't looked into background vs on-demand use of these all that much. Maybe somebody has?