The Grado SR80is are the best I've heard to date, and very tollerant, even plugged into pocket sets - though I have heard a couple of units (CD players) where they were not quite as good with (though not actually bad). The AKG 702s I have read definately need a decent headphone amp, but I wouldn't take anybody's word for it if I had the chance to audition some options - and if you're spending £100 plus on over ears then I would hope a dealer would let you try and compare. Having heard headphones costing up to £250, the SR80s at £112 hold up very well (albeit they are open rather than closed).
+1 for the Grado SR80. Relatively cheap and easy to drive. Nice soundstage and quite exciting, will be great for music, movies, computer games and what have you. I am not sure I agree with an earlier statement that the HD6xx are any good for movies/games, they are quite laid back. In saying that, if I had to listen to an action movie or play computer games (which I don't) for a couple of hours, I'd choose the Senn's to avoid a migraine.
I own the HD600 and HD650 and really wanted the HD800, but in the end I was bowled over by the Grado PS1000 and settled with them, even though I wanted the HD800's to win. In saying that, I was never really satisfied with the PS1000's after I bought them and spent more time with them, as said somewhere else in this thread, they can be somewhat OTT and bright, very sensitive to partnering equipment. I finally paired them with Icon Audio's HP8 valve headphone amplifier and now they are perfect and I will live happily ever after. I don't think I will be in the market for headphones in the next 20 years or so...