One of my favorites is to masturbate between my wife's breasts. She folds her breasts around my erect cock and watches while I pump it back and forth until I cum. We both really get off watching my erection slide between her beasts, and she especially enjoys seeing my semen shoot out onto her chest. She usually gets almost over the edge when I cum, and then masturbates herself to orgasm - sometimes several orgasms - right afterward.
We do it in different ways - sometimes I'll pull out and shoot onto a tit (she gets to pick which one), sometimes I'll shoot onto her face, and sometimes she'll want me to ejaculate into her mouth. She will swallow too. It's fun, sitting in a restaurant, to look at her face and realize that a few minutes ago there was cum right there - or to know that my cum is sitting there on her throat, her chest, or on a tit. I get hard in restaurants just thinking about it. A couple of times she has teased me into jerking off under the restaurant table (in case you're wondering, cleanup was with with paper napkins which she brought along for the purpose).