I've had a set of Panasonic RP-HT1000s for about two years now and they're by far the most comfortable headphones I've ever worn. Nice big cups that cover my whole ear and a self-adjusting headband that adjusts everytime you put them on or move them around on your head. I've worn them for 6 or 7 hours at a time and they're still as comfortable after that as the first 10 minutes I had them on. I don't know how they sound compare to things like Grado or Sennheiser, but they do sound really good, in my opinion.
I got mine for about $50.