Diigo!

I discovered Diigo through LifeClever the other day and have just been in love with it. Diigo is essentially an advanced version of del.icio.us. You can leave comments on a bookmarked page for others, highlight text, leave a sticky note, and of course tag. The advanced social features are great, and Diigo makes it easier to see what my friends are bookmarking from a central login page much like facebook's newsfeed. Check me out on Diigo!