Ok, we're all different shapes and sizes girls, which is why sometimes a generic bikini style just won't do. If your a AA cup your going to want a boob boosting style to give you that extra confidence on the beach, and if your a DD+ cup then your going to want support for those puppies and it's actually quite difficult to find DD+ styles, particularly if your small everywhere else. If you were to go into a highstreet store and try on, say a basic string bikini, you'd have to get a much larger size to accommodate your bust which would leave you with huge baggy bottoms, so you need to go for mix and match styles that you can often find in catalogues and online where you can pick say, a size 14 top and size 10 bottoms or go for a specialist DD+ style and brand like Bravissimo, figleaves are great for stocking DD+ bikinis, and probably the best place online to find DD+ bras too as they have a huge selection to choose from. http://www.figleaves.com
And for those of you smaller girls that want a boost, (i can sympathise as i was an A cup for years before they suddenly grew when i turned 19 and this was before gel bras or chicken fillets existed, so i used to stuff shoulder pads down my bra!) i have found a fantastic website that specialises in gel filled bikini's and bras for smaller busts, http://www.maxcleavage.com the sizes start from 30AA (like the one pictured far left), but their gel bras also go up to a size 38DD for those of you bigger busted girls that like the look and feel of gel bras, personally prefer these even though i'm a 32DD as they give a fantastic shape under clothes and give great support.
Tip - It's really important to get your boobs properly measured at least once a year as our body's change all the time due to weight gain/loss, hormones, and age, and according to surveys, a whopping 80% of women are wearing the wrong the bra size!