Flickr is a photo sharing website with tagging capabilities. To register, you just need a free Yahoo account. There are some storage and uploading limitations with the free account, but you can upgrade to a Pro account for only $25/year. See this help page for a more detailed comparison of the two types of accounts. Institutions can sign up the same way as individuals.
Libraries are using Flickr for virtual library tours and tutorials, promoting events, networking for marketing and other ideas (see the Libraries and Librarians group). Since many of the pictures have a Creative Commons license, you can also search for images to use in marketing tools and on websites. In our groups, we also talked about using the site to get help in tagging archival photos, and for marketing your digital archives by funneling people through Flickr to another site.
For more ideas, see the following resources;
Del.icio.us is a social bookmarking site. As one person at the table mentioned, you can get there from delicious.com, which means you don't have to remember where the dots are! . At its most basic, it is a way to keep all your favorite sites (bookmarks) in a web format so that they can be accessed from any computer. Beyond that, del.icio.us allows for sharing web resources with co-workers or other groups, and exploring favorite websites of other users. Bookmarks can be easily exported from your current browser to this online account, and you can tag them with metadata for easy retrieval.
RSS feeds can be set up to export all of your tags onto a blog or website, or straight into an online classroom. Feeds could also be set up to identify new items in a particular subject, or to follow a new technology/trend. Also look at recent and popular websites, and user's notes about a particular website. Make sure to set up the browser buttons for making easy additions without interrupting your workflow. The settings page (which you can access when you are logged in) contains most of the details about how to do things, or see the tutorials below.