avant rocks! i installed this weekend and it's really great. it's IE based so no compatibility issues. pure gain. regarding firefox, you can get a spell checker with google toolbar, so it's not that much of a new concept.
btw media player 11 is now officially released too. personally, i use the KLite mega codec pack and their modified version of media player classic. so i'm not even going to bother with v11.
Try FF2.0 as well. The things I like most about it are that the advert removal is much cleaner than in the IE/Avant environment and I can create a tidier browser than I've achieved previously. Note that the two folders in the picture are from the "Bookmark Bar" and I don't label them as I know what is included (they are basically groups that I open as groups).