I won't use a thing except IE. I spend an insane amount of time on the web and a lot of that is designing / developing, so I don't want or need the problems of Netscape or Opera. (Debate it all you want, I still won't use em.)
That said, I use Crazy Browser. The underlaying IE render engine combined with the tabbed browsing, popup stopping fun of Netscape is unbeatable in my eyes. Only thing it won't do is true popup windows. 99/100 times it simply opens a new tab which is good enough for me. (Popups -rarely- need to be popups)
For a lot more info there's a
rant over at my site, or you could just check out the
official site.