Instead of entering your Pandora username and password on a third-party site, you can use a Firefox plugin to scrobble your streams into last.fm. I love that.
Speaking of extensions, my library finally has a LibX toolbar plugin and it's great. I just added it today and I'm already instinctively going to it instead of constantly going to the homepage. The only problem is my toolbar is getting crazy crowded. Even though I use blummy, I have 21 bookmarks I use so often I need one-click access to them. If the meebo link wasn't staring me in the face, I'd forget to log in every day and I need to leave it up if IM at work is going to be useful. It's weird how everybody works differently. I like as few windows as possible, so I keep many, many tabs open as I work. My dream would be for everything in the universe to work like a combination of firefox and tivo.