bit of an audiophile here
Sennheiser 565, 580, AKG 710 and thinking about Denon AH-D5000s at the moment...
At the low end, I had some Porta pros for a long time and they were great. The Sennheiser PX100s beat them, and can be had for under 15 quid. I'd go for those over the PX200s, which while they have leather pads, don't sound quite as good.
www.headphone.com have refreshingly honest reviews, even stating some of the stuff they stock is rubbish compared to others. Great place to start your research.
However nothing beats an actual test, just get a decent sound source, plug both sets in and compare them. You'll be amazed how good a good set can be.