It all depends what 'type' you want. Also what price you are willing to pay.
WARNING LONG POST AHEAD (go get a coffee).
I'm really liking the Audio Technica 7 for in ear 'non-isolated'
see here for more details
http://www.audio-technica.com/cms/he...4b8/index.html
They are good straight out the iPod and also respond well to amping especially the portable amps. The price for me was £35 but a whopping £12 postage as is was from abroad off eBay. These are very comfortable and flexible don't know about long term durability had mine about a month now but look well built to me. It beats my previous favourite the Sony 21's
The senn mx500 is 'ok' but is not that good when amped.
For in ears 'isolated' the shures are very good but go with the e3c as a minimum (again bargains to be had from eBay) I have the e5c and they are really good but at a high cost.
The Etymotic ER•4 are also good but cost is c£150. I hear the senn 300 are good but I haven't personally heard them so can't comment.
'Over ears' the px100 and px200 are good and are fine when amped as well. I personally liked the px200 more for the better bass output when listening to R&B, Rock, etc.
The full size cans for me has to be Grado's. I've got the RS1 which are brilliant again brought second hand so less than half the usual price which took it into the Sennheiser HD650 new price range. But also look at the range sr80 upwards.
I like the Senn HD600 and 650 but don't think they compare to the Grado for my ears anyway. I have just ordered some AKG701 to try and knock the RS1 off its spot.
So to summarise
if you want non isolated in ear go for the Audio Technica 7 will set you back between £40 - 50 but it has a few advantages over it's cheaper rivals one is it responds better when amped, two comfort and last and most imoportant sounds better. It will also stop you itching for something better because so far I haven't found anything for that earphone type that beats it.
If you want isolated in ear shure and the ety I can praise as I have heard but not heard senn cx300. Go the eBay route for the e3c and ensure you have proper fit in ears if wearing. Note the disadvantage of this ear phone type is if you travel a lot you can't really hear traffic sounds or people calling you etc so this is more suited to sitting down and just being lost in the music
Ok over ear I hear the koss porta pro are very good and some of there other products for overear but again I cant comment. I have heard the senn px100 and 200. The 100 leaks more sound to people next to you but the 200 do not (much). The 200 can get a little sweaty on the ear (well mine anyway).
Ok for serious listening I would go with auditioning the senn hd600, hd650, Grado 80, 125, 225 or 325, Beyer 880. <--- These will respond very well to amping in fact best to use them amped. I say these as you asked the question about the quality vs cost curve
Ok the way I see it is (just in general not an absolute rule) . £10 - £30 you can get 'reasonable' headphones
From £31 - £90 you can get good headphones (again I'm talking eBay or second hand where you can get the Grado 80, Koss Porta, Audio Technica 7. Then £91 - £200 you can get the serious headphones. All of these offer a very noticeable jump from the previous group however the costs keep on doubling roughly after that so you start to get into the Grado RS1 at double the cost c£400 eBay and others from Sony 3000, etc but it's at this point that a lot of people will say is it worth it only you can decide
So I would say go all out to get the best now that you can afford will save you in the long run. Maybe have two sets of headphones minimum. The first would be for your travelling, are more descrete, portable etc and the other one of the 'serious' ones. Like someone already said I don't see the point of settling for the £20 - £25 ones. Please don't say you can't afford double that amount because you can. Your drinks, cigarettes, money you waste, is probably another £25 'student' or not. The reason your on this forum is you want something decent so get something that will be good in the long run.
If you think they are too expensive make them a birthday present from someone, go get a job

and pay for them. This saying is true "you buy cheap, you buy twice".
For home go for open back designs full head cans as mentioned above or similar for travel decide whether you want isolated or non-isolated. If non isolated decided if you want in ear or over ear.
I have three (but thats me) that I use often. The RS1 for home. The e5c I try to use as often as possible if I'm not going to be disturbed at work then they go on and are amped. If I will be disturbed I use the Audio Technica 7.
Hope this helps