Gemsta.com - Great. Allows storing of links, videos, images, text, products, & more. Good bookmarklet; Toolbar not Firefox 4.0 compatible.

uvouch - social networking site. due to high spamming activity links can only be submitted through fan clubs. clunky bookmarklet. many ads.

favbot - you can sign up but you'll have to still wait for an invitation before you can try it.

stickr - allows one to stick notes directly to websites; similar appearance to twitter. good for notes & sharing.

LinkCloud - attractive visual interactive bookmarking; site icons can be clipped & structurally laid out. Good Firefox plug-in.