I don't have a favorite swim website, I usually find them in stores. But I would suggest going on Victoria's Secret website, I think they're having a swim sale right now!
If you want to go in-stores, I would suggest H&M. Their swim collection is amazing. AND the prices are low.
I'm glad I'm not alone on my search for the perfect swimwear. I cringe having to try on swimsuits in the store inside a tiny dressing room with bad fluorescent lighting. Online shopping has given me the ability to try on items in the comfort of my own home.
Victoria's Secret (http://www2.victoriassecret.com/landing/?cgnbr=OSSWMZZZZZZ) has the sexy appeal on swimsuits.
http://www.swimoutlet.com is also another site that I like going to when buying swimwear online. They give you visuals of the type of style you can select from.
This season, I've been into floral patterns. Check out this floral print swimsuit from Land's End (http://www.landsend.com/pp/ShapeWearFloralTankSwimsuit~206392_593.html?bcc=y&action=order_more&sku_0=::BLF&CM_MERCH=IDX_00002__0000000135&origin=index).
Hope this helps.