Just won a set of Sennheiser HD600 on ebay. I am very excited. $227 total. Said used less than 5 hours. Box and all. Look very nice in the pictures and the seller said they were mint.
I have a pair of HD580's, which i believe are almost the same headphone (some say the same drivers, but I have yet to find definitive proof). I absolutely love them. The only thing I've learned is not to make any level choices using them. Everything is so damn clear that I find I can't make the right decisions (e.g. mainly if something is too soft, I can't tell because I'll be able to hear the part so clearly that I don't feel the need to bring up the level).