The Internet Explorer 7 Team posted an amazing list of must-have Add-Ins for IE7. Some I'd seen, some were new, and I'm using almost all of them now.
I have both IE7 and the Firefox 2 beta on my laptop, and I must say I am very impressed by both. Two of the must-have add-ins for IE7, Inline Search and IESpell, drop into IE7 the two missing bits of functionality I coveted in Firefox - the search filter bar at the bottom of the screen, and the spelling checker. Although some reports are that Firefox renders some sites more quickly, one IE7 feature that I find greatly increases my web surfing productivity is the Quick Tabs view (hotkey: Ctrl-Q).
What are your favorite and must-have browser Add-Ins?