Basically I've got no real clue, so any pointers as to where to look would be appreciated.

What I'm after are some headphones to wear at uni/work/home-at-night for extended periods of time whilst working. Sound quality should be decent, but other areas of similar importance are things like a lack of leaked sound if I'm to use them in the library and comfort when worn for extended periods of time. Being foldable would help considerably too. Source will be iPod/iPhone and laptop. If they come with a case to transport them in that'd be a bonus, as they'll be moved around quite a bit.

Noise cancelling would maybe nice, as I like my noise-cancelling in-ear Shures, but not critical. Budget is £70-120 (absolute maximum).

I got a pair of Sennheiser PX-100s, as I can't abide in-ear things. They fold up, have a nice hard plastic carry case, but have a weakness around the cable-plug joint. I've sat on them, slept in them and generally abused them yet they still survive.

They cost me £16. They're great for the stuff you describe, generally sound good to my cloth ears, but lose it quickly outdoors I find as they're open-backed.

I had a quick squint at Amazon, and the more expensive versions seem to get reasonable reviews.

EDIT: Just looked at the PX-100 on Amazon - someone is having a huge laugh! £60?!? They have go to be joking! I noticed this yesterday when I scoped out the current price of an old lens I've got. I bought it for under £100 a few years ago, but it's listed on Amazon at £350. In no possible way is the lens in question worth that much. There's something awry somewhere.

I use the Sennheiser CX 400-II Precision in-ear headphones, which are really decent, cost just shy of £30.

I would warn you to be very careful when buying headphones. For example, Amazon sell those for £30, but some sellers somehow manage to list them for £10-£20. Now I can't say for certain that they're fake, but I've been shipped many a fake set of headphones from third party sellers on eBay and Amazon before, so much so that I can only recommend buying them direct from Amazon or going into a real-world store and purchasing them.

I've got a pair of Sennheiser HD205 Closed Back Headphones which I think I paid about £50 for.
I was wearing them last night, whilst working on the PC, and the volume was loud, but nobody else in the room could hear them. Sound quality is OK, I think, but they'd probably sound better plugged into something a little better than the computer...

Hope this helps.