Diigo (http://www.diigo.com/) is an awesome tool for bookmarking, but it goes beyond that! That is like saying a Lamborghini is just transportation. (If you have ridden in one of these things... I need to get to know you!)
This is a tool you should be using personally as well as with your students. It allows you to bookmark websites, as well as highlight content on that site. It's a cloud based organization system. They have great browser add-ins that add all of the functionality, as well as an iPad app (http://goo.gl/XCNz3). (Make sure you try the Diigo Browser http://goo.gl/iOqAB, it is one of the best browsers for the iPad. Formally it was the iChromy browser for the iPad.) You can even download the content for off-line browsing.
If you are a teacher, apply for an educator account: http://www.diigo.com/education
Many services are free, and they offer some premium features for a low cost. Check it out... and add the Google Chrome extension here: http://goo.gl/RulSI (Not using the Google Chrome web browser??? You should be!)