I have a pair of Samson RH600
http://www.samsontech.com/products/prod ... &brandID=2
These are the second of two that I have owned, and I do use them extensively for mixdowns. They don't "lie" to me. I love these phones, and will continue to use them as long as they are available. I wore the first pair out completely.
The process I use is, I'll do all my recording, and preliminary mixing through my M-Audio BX-5A nearfields, then a thorough check using my Polk 10 Studio monitors, then the Samson cans, and finally the car stereo.
I've had My 01 Honda Accord for many years now, and I'm very familiar with the stereo, that helps a great deal.
One last check in the CD player of the 06 Toyota I drive for work, and if I can't hear any major problems, I call it ready for critique.
I don't hear well anymore so I can't fully trust my ears, therefore I rely on my friends to tell me if there's to much high end, etc.
Oh...Almost forgot, I often listen to a final mix using cheap iPod/Walkman type headphones/earbuds, just to see how different the mix sounds.

Can't hurt!