Ultrasone are overpriced - at any level.
For under 200$ you can have a good pair of Sennheiser or ATH M50. And these cans also measure well.
IF you have 500$ to spend Sennheiser 650 comes to mind - very very good.
Beyer dt880 is also a very good can - 32/250/600 ohms - I'd get the 32 ohm ones to drive them with an iphone/ipod/iwhatever.
As for amp - it only makes sense if you get the Senn 650 - otherwise try getting something you can drive from an ipod.
Don't listen to all the hype around head amps - the ipod is king (this is coming from somebody who owns a Benchmark hdr).
Or - buy a cheap amp