theOutnet is awesome! I've gotten three pairs of Louboutins from them, as well as a McQ skirt and jumpsuit, See by Chloe trousers, Karl Lagerfeld jeans and belt... all authentic and wonderfully priced. And they have an excellent customer service team, too.
Typically, they "further discount the discounted stuff" on their "weekend shop-in" sales. Every Friday, they have a theme (like workwear, or casual wear, party wear, or the like), and they offer an additional 30%-50% on a selection of items that fit that theme. I think that's the only time they ever really further the discounts on things, though, so if there's a piece that you have your eye on, it's really up to chance whether you'll see it discounted further.