callum,
Lots of good advice here. One of the key points is to make sure you try one out in the air for an hour or two, before buying. Ten minutes walking around a store looking like a wannabe is not enough!
I'm one of those people who finds a DC excruciating to wear for more than a short while. I have a Lightspeed Zulu 2* that I have worn for flights of up to three hours with no problems. For non noise-cancelling headsets, I like the Peltor.
* A minor problem I'm having that needs fixing is that the boom mike is loose - it acts like a G meter in steep turns!