I have an ex who has been with hundreds of men (really) and yet until one afternoon at home she had never watched a guy jack-off. We were naked in our living room and ended up seated across from each other. I told her that I would like to watch her play with herself which she started doing. Of course that was hot, so I started working my dick. We kept at it for a while and ended with both of watch the other cuming. It was so HOT. What really surprised me was when she said that she had never seen a guy jacking himself, much less cum, shooting off (not that I could shoot that great at my age). She usually had the guy riding her banging away and shooting his load in her cunt.
Needless to say, we did this some more. I really liked watching her using her vibrator on herself too.
This to me is a fantastic way to have safe sex. No touching, just hot images and sounds.