One of the men recently posted a paragraph about how he and his wife enjoy having him orgasm between her breasts. My husband and I enjoy this too. I understand that I'm both unusual and lucky that I can get very excited just from breast stimulation alone. I get quite excited, quiet close to orgasm, watching my husband have sex with my breasts folded around his erect penis.
I also enjoy breast self-stimulation. It can be a very important part of masturbation for me. At times I will go braless when I'm shopping or just walking downtown. Other times I will wear a bra with the tips cut out so my nipples show through quite clearly. If I've done either of those things, I usually masturbate my breasts a little while driving home. If I'm sure it's safe, I'll even expose one breast, at least the nipple, while I drive.
Once I'm in the apartment I'm already pretty far along. Removing my top (blouse, sweater, whatever) I usually start right out with my nipples, gently squeezing and stretching. I like to watch myself in the mirror. I'll often oil my breasts and very gently caress them, base to tip, just with the tips of my fingers. I start with the tops, saving the more sensitive outer sides and lower parts for a few minutes later. I finish with my nipples, using my thumbs on top and two or three fingers on the bottom, rapidly stroking the nipples base to tip several times for each breast caress. My nipples get very hard and erect, but I can't expel milk any more like I used to be able to do. I think it takes about 10 minutes of breast stimulation to get almost to the point of orgasm. Most times I finish up with my fingers working my clit, but occasionally I can get all the way to orgasm just from breast stimulation alone. I've read that only 2% of women can orgasm just from their breasts, so I know I'm lucky.