Opera 7...
I just love the mouse gestures and the fact that on startup it loads the pages I had open when I last used it...
Netscape 7.1 for the email client and the fact that my bank prefers it for internet banking...
It's also nice to have when I don't want to load 6+ sites, but just check something out...
I've also got netscape 4.78 installed for support purposes... The only thing I use IE for is windowsupdate, and I'd change that if I could, but alas........ (And no, a new frontend won't be enough)