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Erm... Sennheiser is imho safe choice... but frankly speaking I don't think that you need advice.

You are looking for headphones up to 30$, right? As long as you pick up good brand as Sennheiser or Audio-Technica you should be fine. Really you won't notice that much of a difference between cheap headphones models (I mean only between those from good brands, and btw ignore all “stylish” and “fashionable” brands).

I swear by the Sony MDR-E818LP headphones.

I've tried a whole lot of others but the bass is always overdriven and muffles other sounds out, or the treble is too tinny and dominating. Those ones I use hit that sweet spot for me, but apparently they've just been discontinued. Try to find what they've replaced them with (likely an updated build of them) and consider going with them. They originally sold for between £10-20 but had excellent quality. Their only drawback was that sometimes the wire could be fickle, and an occasional pair would get a lose connection after only a few months of using them, causing one ear to die. Though they usually lasted me a good 6 months before any signs of degradation. I suppose my bunching the wires up tightly to put in my coat pocket never helped that though-

Superlux HD668B Dynamic Semi-Open Headphones just read their reviews ;D

Woah woah ..... why is it hard for you guys to read ? The OP is asking about EARPHONES and everyone else (other than Uroboros ) is speaking about HEADPHONES !?

On topic though, Personally I've used an entire boatload of different earphones ( i have a tendency to misplace them :P) but I would recommend Sennheiser as a safe go to brand. Not to say others are bad. I'm currently using Sony Universal All Round In-Ear Headphones which serves my purpose and it was something like GBP 7. Unless you are very finicky about sound quality this model should do ok. Though my friend who has this earphones did say it has low bass but otherwise it is a solid product.

As far as I'm aware Sennheiser, as others have said, is relatively safe, and tends to focus on quality rather than gimmicks/trying to be cool, so it seems like a good choice.

I have not owned these 2 earphones I am about to suggest, but they are well received over at the head-fi forums.

Xiaomi Piston
Brainwavz Delta

Lolz...I bought 25 Evike "EAR-SOFT MEGA BASS" earphones when it was $1 each...it's quite shitty but I can probably sell them for like $5 each or something so it'll all work out. lolz

If you ever go on a long distance flight, you can keep the airline headphones. I have a few of those. :D Shineh

Increase your price range. I would never skimp out on a quality pair of cans or earphones. I just picked up the sennheiser ie 60's and They are way out of your price range but consider getting an expensive quality pair that will last.

I haven't tried Sennheiser, but I've had good luck with Skullcandy ink'd buds. They've got great audio quality to my (limited) ears, better than some more expensive ones I've tried out. Also, they have a mic built in for using with your cell phone and such (but it's small enough, if you don't need it it doesn't get in the way).

I've never liked earbuds (they don't tend to stay in my ears) and on ear, or over ear, headphones start to bother me after a while. I found some Aftershokz at Office Depot last week for $24. They don't have them online, but the stores seem to still have them, and you can go in and try them out. Twentyfour dollars makes them less than half price. The bone conduction is very very cool. No good if you want to block outside noise, though.

I have the Audio Technica CKM55, but the model and the CKM500 variants are usually in the $50 range. Probably the best value for money in that price range.

If you want to stick to your budget, the Sony DREX61IP seems like a great choice. They sound pretty good, but just be careful around these earphones. $27.99 seems like a great deal, and you can get a refurbished one on Amazon for $19.99.

Bestbuy for 20$ :D
http://www.amazon.com/Brainwavz-Delta-IEM-Earphones/dp/B00FSA8VQ2/ref=sr_1_1?s=electronics&ie=UTF8&qid=1398180873&sr=1-1&keywords=brainwavz+delta

Monoprice. Monoprice. Monoprice.

If they're in an improvements over the Sennheiser CX200, then yes get those.

I have this cheap earphones and are one of the things with more quality/price that you can buy.

Maybe with 30€ you can found a better sound quality, but this earphones worth it