I just bought a strapless bra today. I don't mind straps showing on simple tank tops, but I have a nice silk tank, and I bought a satin and crochet tank the other day, and I needed a strapless for both. I asked the saleswoman at Macy's if she could suggest a strapless, and I could tell she was happy to help. She said her daughter had a small chest like me, and she gave her a Calvin Klein strapless and she just LOVES it. (I figured her daughter was in her teens and just hadn't developed yet. Later she told me her daughter was 40.)
I've never had much of a bra wardrobe. For the past six months I've really only had one bra I liked, and just ended up hand washing it frequently. Most summer shirts have a built-in bra anyway. Besides, I figured I could have one bra and lots of shirts, or lots of bras and one shirt.
Oh, and to all those who said their straps are constantly falling down... I understand enjoying the feminine feeling of having to pull them back up, but I feel sure you are wearing the wrong size bra or your straps need adjusting. That shouldn't happen.