These sites allow you to store, tag and share links across the internet. You can share these links both with friends and people with similar interests. You can also access your links from any computer you happen to be using.
So, if you come across a webpage that you find interesting and want to save for future reference or share it with other people, simply click on one of these links to add to your list.
All of these sites are free to use but do require you to register. Once you have registered you can begin bookmarking.
Each of the sites works slightly differently so use the links above to find out which service best suits your needs.
You can find out more about social bookmarking on Wikipedia.
What are these?