The good folks at cybernetnews.com have a great tip for putting Google’s Calendar in Your Firefox Sidebar. Granted, its better if you have a wide screen monitor for this feature not to crowd out your browsing experience, but for those that like to keep tabs on events and important dates while browsing it’s fantastic.
Another app that I like to keep on the sidebar is Meebo, but there’s a great Firefox extension that takes care the clicking/bookmarking part. Check out these posts in Lifehacker & Cybernetnews for more great sidebar goodness.
Of course, you could also use Flock (Firefox’s distant cousin) to have websites like Flickr, Facebook, Twitter and a bunch of other ones load up on the sidebar.