Plus Size Bra Info has the best measuring method and a very useful brand size equivalency chart.

Bravissimo carries Panache (I like the Tango), Freya, Fantasie of England, along with a house brand that does very well for many people. Do read the reviews of each bra, because if there is any weirdness in sizing or fit, (it's tight or loose, better for round or oval breasts, etc) that's where the information will be, in customer comments -- rather like Zappos that way.