Actually, just two color swatch sites that I heard about recently. Both are free to join and you can design palettes, browse palettes and download them in different formats. First up is Coolors.
This has a nice interactive palette maker and the site layout is very swish. That's my contribution in the top left corner. The export options are these.
However I think I'm leaning towards Color Lovers, this site isn't as sexy but the feeling of interaction is strong as they feature a forum, a blog and groups, users can also up-vote swatches and make comments.
Another plus is if your swatch uses a new color that hasn't yet been used, you get naming rights. Pretty cute. I give the world Blue Salt and Young Peppermint.
Here are the export formats.