The newest bookmarking site I have found is pagekeeper. Like the other bookmarking sites, one of the most useful aspects is that you can search other users bookmarks to find useful resources for integrating technology in your classroom. http://pagekeeper.teachingmatters.org/user/1536
Another useful bookmarking site that offers a huge amount of resources is livebinder. In livebinder your resources are in a notebook with tabs. You can also search for livebinders in the area you are interested in.
One of my favorite bookmarking sites is Symbaloo, This website can be used by students and teachers to access resources for specific themes or units. You can also search for other teachers webmixes.
Of course their is always delicious, but it is often blocked from educational networks.
Livebinder is a website that allows you to share resources/links in the form of a notebook. It is blocked is some districts, and often by students.
I haven't tested this bookmarking site in the school districts yet, but I am hopeful that linkable is not blocked. It allows you to easily link and organize bookmarks.