38 C (or 36C if it's particularly stretchy.) Of course, the problem is that I buy cheap bras, so they don't fit as well as the $70-$80 Chantelle bras. But it's nice that I wear a size that I can buy off the rack, so at least now I know. I also got a very nice Calvin Klein strapless push-up bra for $44. It looks great, it's as comfortable as a strapless bra can be, (really, it's not bad), and it was a totally painless experience.
Also, I would like $500 to fall out of the sky so I can get an entire new bra wardrobe. And I'm ONLY allowed to spend it on new bras.
Also, I have two strapless bras in excellent condition from Cacique. They're barely worn, and they're a size 40C. But I think they're closer to a D cup. They also have adjustable back straps on either size. I don't have the convertible straps that went with them, but they were crap anyways. If you're interested and you're in the States, email me at my user name @gmail and I'll send them to you.