I was recently invited and signed up to Cocosa, "...an invitation-only fashion destination offering members to exclusive private sales of luxury brands...". It is still very new but a very slick site! The images of garments and accessories are all very clear, so if you like your luxury brands and also like a good, and extremely heavy discount from the original price, Cocosa is a wonderful place to go. Because it is invitation only, you can become a member if you enter 'nuvonova' into the 'I've been invited' box... this is only available until the 28th November 2008, after that, you will need to find someone else who has an invite code, or you will need to go on the waiting list!
As it is still new, I feel the site is still missing a lot of content, but I can definitely see it heading towards being a fantastic virtual sample sale destination - so you don't have to put up with the freezing cold if you're after sample sales in London! The site also has an amusing countdown timer for when new garments for a specific brand is being launched, and how long left you have to buy. Again, this has a similar concept as samples sales do, as of course, they're always only on for a couple of days, sometimes just one day, and sometimes just the one day that you can't do!