Update: I stopped using all these headphones a few weeks after testing them. Noise isolation is a nice thing to have, but solid across-the-board sound is more precious to me. That said, my earbuds of choice are Apple's $30 EarPods. They're affordable, sound great, and have survived multiple traumatizing experiences in the washing machine. I've even dropped them in my water bottle by mistake. Of all companies, I didn't expect Apple to make the nicest earbuds, but I prefer them to my old Sennheisers. As far as noise isolation goes, they're nothing special, but they do block out a good bit of background noise in the coffee shop so they aren't worthless.
So, cheap in-ear headphones. I don't like them. I don't like the appearance or sound of Skullcandies nor do I like the feel of most earbuds, especially the ones with the over-ear loop — rubbish. I decided to buy a set of Monoprice 109927s a few days ago just to see how well they actually perform when compared to Apple's EarPods, which are my economical headphones of choice right now (in-ear and over). Then, since they looked really nice, I also purchased some Sol Republic Amp one-button model, which are twice the price of the Monoprice ones, but actually look nice.
The first thing I must address on these headphones is the appearance. They're downright ugly. I was scared to be seen with them outside my house because of how little they fit my setup: MacBook Pro, Magic Mouse, a Dropbox t-shirt, red Vans shoes, and ... steampunk-like earbuds? I would not recommend buying these for their visual appeal, because you'll be sorely disappointed. The really strange thing is, for the noise isolation that they offer, these earbuds are very comfortable. I'm used to putting in earbuds feeling like they're going to crush my head. The Monoprices are barely noticeable once you actually put them on. At first sight, I expected them to poke the edges of my ears and annoy me, but they did nothing of the sort. After a bit of use, I preferred using them over the Sol Republics because they didn't get me a headache.
These definitely have "enhanced bass", but not the kind I enjoy. Kick drums in songs like Avicii's "Wake Me Up" sound horribly muddy. That can be said for the rest of the audio, actually. The entire mix has one tone. You can fix it with an equalizer in iTunes, but that's not the point of good headphones. When I put the Sol Republics in after using the Monoprices for a bit, I instantly noticed a difference in sound. Where the Monoprices had a hard time hitting certain frequencies, the Amps sounded fantastic. I still found that the overall clarity in both headphones was much less satisfying than in a $100 pair of Sennheisers. Then again, Sennheisers don't have enough bass for my taste. Unfortunately, neither of these headphones gave me the best of both worlds. Sol Republic's came close at first, but still sounded too low-mid-focused for me. After a bit of comparison, I found that Monoprice's offered the best clarity, but the bass always sounded distorted. And I don't have a problem with bass: I have to 10-inch subwoofers in my car. There's just a difference between a good mix and a muffled one. Both these headphones sounded like I didn't have them all the way in no matter what I did.
As for noise isolation, I found these earbuds to have the best in their price range. The Sol Republic Amps trumped them, but they are twice the price. I preferred using the Monoprices, though, because they isolated noise nicely while remaining comfortable. When I put them in I didn't feel completely isolated from the world. That may seem like a weird way to judge the headphones, but I enjoyed complete noise isolation without feeling it. The headphones sit in my ears like the EarPods do, which is perfect. On that note, I'm not sure they would fit everyone. I gave my sister my Sennheisers and she had to replace the ear tips just to use them. I suppose judging them by their appearance wasn't the best idea after all.
Overall, the Monoprice earbuds are louder than most headphones. I have to turn them down to half the volume of the Sol Republics and EarPods so I can listen to them. That's not bad, but it catches me off guard every time. I really enjoy the Monoprices, despite their muddy bass and dull frequency range. They are easily the best earbuds you can buy for $10, noise-isolating or not. I am very surprised by how well they isolate noise, too. I would happily recommend them to someone who works in a loud space, but not to anyone who jogs — they easily fall out of your ears.
The Sol Republic Amps are very disappointing. They don't sound that good for the price and stick out of my ears too much. The way they hit certain frequencies makes me cringe. Listening to "Punching in a Dream" and "Young Blood" by The Naked and Famous for a test run, I found the Monoprices more tolerable, but neither set very good. Most of the high frequencies were drowned out by the mids and when they weren't, they pierced like a knife in the dark. It's not all that pleasant. I wish they sounded as good as they look, because they're actually attractive.