I've been thinking about putting together a list for awhile, because so many people ask me about it. So this is my first attempt. If this ends up being useful, I'll keep updating it with new, different, trusted sources for online bra shopping. Where do you shop online that you love? Comment with your favorites and I'll add them to the list!
Bare Necessities - Band sizes 28 - 58, Cup Sizes A - N - This site pretty much carries it all. Any size or style you need, they have. Huge size range, from small to large. I especially love their selection of swimsuits with real bra sizes. They almost always have something on sale.
HerRoom - Band sizes 28 - 58, Cup sizes A -N - HerRoom is another huge online bra retailer with a decent swim selection. There is some overlap with Bare Necessities as far as brands and styles, but they carry a few that BN doesn't have. I'm not as impressed by their sales, but they are still a solid option.
Wellfitting - Band sizes 26 - 50, Cup sizes A - O - Wellfitting is fairly new to the game, but I like their mission. Their selection may seem small, but just about every item is offered in a massive range of sizes. They have super cute prints (unicorns and kitties!) and fun colors. I love that they use a wide variety of models.
Impish Lee - Band sizes 28 - 40, Cup sizes A - J- Impish Less is fun because everything is customizable. If you want to invest in something truly unique, this is the place to do it. You pick from their designs, then customize all the details. What you pick determines the price.
Nordstrom ( Band 28-48, Cup A - K) and Bloomingdales (Band 28 - 46, Cup A - G) - If you insist on shopping with a department store, these are the two I trust the most for bra shopping. They know what they are doing and have a decent selection. Their in store is more knowledgeable and helpful than most, so if you live near one, they're a reliable brick and mortar source as well. Fortunately they have both figured out online shopping so they are reliable on that front too.
Gilt and Rue La La - (sizes vary) - Boutique shopping sites can be great for lingerie at discount prices. It's also a crap shoot on what sizes, brands, and styles they're going to carry. These two sites are the ones I have had the best luck with. Once you have a brand you know you love, it's easier to shop these sites and snag a great deal. Return policies are not always great on these sites though, so keep that in mind.