I'm a dainty 36D but used to be a double-bagger until I found the Champion doubledry... forget exactly which one.

I can't wear it forever, though, without the ribs starting to bug me. I wear it under my tri suit which is a big improvement over having to put one on over the bathing suit in the transitions (I was afraid I had so much cotton/lycra that it would drag me to the bottom of the pool :-)). At least there was a lady hanging 'round who could give me an extra tug... the poor bike-watcher was a teenage kid who probably would have died of embarrassment