I know it’s still in beta, but Firefox 3 is looking really really nice.
Really fast, funky drop-down preview/autocomplete thingy in the location bar, nice styling and look and feel. Lovely.
Give it a whirl from Mozilla: http://www.mozilla.com/en-US/firefox/all-beta.html
PS It seems to co-exist fairly happily with FireFox 2 under Windows.