I can only use headphones because the speakers I have aren't made for audio monitoring - they're gaming speakers - and I don't have the money for monitors.
That said, I don't have money for $500 headphones, so I just compare parts of my tone to those on pro recordings through the same headphones, which gets me into the ballpark and since I hate mixing all I have to do is try and line up the tracks and send it off to MP3.
Jeff