I have the AKG K701's. They are the only reasonable $ contender with hd650's some preferred the k701, some the hd650s. I love my 701's and with either set you choose...definately need to get a dedicated headphone amp. I got the little Dot II++ and I think I paid 150, looks awesome and sounds awesome too...has a jumper for adjusting to higher or lower impediance headphones. The 701's have a real great fit and the sound seems relaxed and if anything they seem to emphasize the midrange but with a smoothness.
I got the k701's for right under $300 off of amazon. I kept reading about how long they took to break in but thought, How bad can they really sound? I did not like the sound at all when I first got them...days of breaking in later and they made me a true believer of the infamous "break in" period. I highly reccomend them!