If I have a dress that has a low back or something where I can't really wear a regular bra, I end up taking a sports bra, cutting it up and sewing it into the dress. It is easy to hide that using the side seams of the dress to sew the bra onto. The tricky part is getting the right tension in the band and getting the top to line up right so that it doesn't show.
I currently am a 36D and I am finally at a point where I feel somewhat comfortable wearing a regular bra if I have to (wore one for the last time I took senior moves and for our show this past year - moves was scarier to wear it for than the show!! Probably because I already feel self conscious that I am taking senior moves as a 31 year old and the judges around here oftentimes are not entirely supportive of adults skating). I was at one point a 38DD, but I have lost about 40 pounds total and about 20 in the past year - and in the last year, I have gained a lot of muscle, so I have no clue where that puts me in terms of real fat loss. My measurements are still going down and I am hoping that my chest goes down more. I would love to be a 36C...and if they go smaller than that, BONUS! I doubt that will happen since most of the women in my family have larger chests (but then again, many of them are overweight too, so I can't really compare), but a girl can dream, can't she?