Another alternative is:
Bower & Wilkins P5
I'm thinking about picking up either one of these.... any thoughts?
Grado SR80 are amazing if you don't mind everyone else hearing your music. I can second AKG550s if you are in that price range. A few months ago I did tons of research and was prepared to spend up to 250$ and ended up with the well-respected Audio Technica ATH-M50 for about 115$. They are tanks and their flat frequency response is what I wanted; also love their austere design in black.
Also, IMHO Bang & Olufsen is more about form over function, but if that is a priority then go for it.
I hated Grado SR80's. Firstly, they have way too aggressive mid-treble and are very "spitty"; it's their trademark sound that some actually enjoy. To me, they sound terrible. The ear pads are foam pieces of shit that are not comfortable at all. The overall build quality is shit, too. The connection points for the articulating pieces are very fragile in their design.
Senn's house sound is very mellow while 702's are very analytical.
If you like a more exaggerated "engaging" sound, I'd go with DT990's. Beyer's have been on Massdrops lately for great prices. I wouldn't go with closed headphones only because they get hot during extended listening sessions, so the DT770's are out. The 770/990's will be more exaggerated on the ends of the spectrum, which may suit your preferences better. The comfort and durability of Beyer's is easily a level beyond AKG or Senn.
Also, I'd recommend playing with some plugin's/EQ to tweak the sound to your preference.
Hi for audio professionals and for the those who need headphones for critical listening i would only personally recommend audio technia http://www.shoppingway.co.uk/brands/audio-technica , i have also heard good of shure but have not tried them.
I would also recommend MUST AVOID headphones like Beats SMS etc