Hey Nell,
I started leaking a couple of weeks ago and after hearing all the scary stories about mastitis, thought I should buy a maternity bra. I'm in a 16DD at the mo and tried on everything they had in my size.
There are some fayreform ones which are pretty good (but they were the wrong shape for me) which you can get in 3 packs for $100. They are evidently very supportive.
I also tried on all the berlei ones, but they were funny shaped on me. Amazingly the Elle Macpherson bra (which I have never ever found comfy as a 14D) were perfect and I have two of them. I am very happy with my "shape" now, the purple one looks lovely under white things, and the straps are really nice. They aren't cheap, but i figure I'll buy these couple of expensive ones, and then go to town on the cheaper ones I'm happy to wear around home/in bed. Target looked like they had some pretty good ones, its just a matter of waiting until they have 20% off again!
Warning - the Elle mcPherson ones are pretty expensive ($55), but like I say, I'm really, really happy with them! Just get fitted properly though - its totally worth the extra money you pay at somewhere like BnT (well not extra money, just never discount, flybuys or anything else!)
Good luck
Fi