Just signed up for boxedup.com. No idea if I'll like it yet as I just signed up, but it looks pretty nifty so far. You add things you want to buy to your "box" and share them around. Obviously it will likely be a solid tool for the holidays... we'll see how it pans out.
Anyway... the whole thing looks like a del.icio.us, but for products. They've taken a page out of del.icio.us's book with browser buttons. This is just a great way to get people to stick with your site after you've gotten them to go through the dreaded signup process:
It automagically identifies my browser and gives me big, descriptive buttons to help me add them to my toolbar. Great. Now I have buttons added to my browser that will make me much likelier to user their site in the future. Their blank slate is pretty hot, too:
A quick, short description of how to use the very basic functionality of the site, and a highlighted way of pointing out the easiest way to import Amazon wishlists (which I'd imagine quite a few new users might have).