Summary

Finally a good set of ear buds that don't cost $100+!!!! Regular price at CC is 69.99 but these were mis-marked and I got them for $20 off. I tried the Sony's at $49 but their mid and treble sounded manufactured, and their cord was too short without the extension (included). I had looked at he Shure brand after seeing good reviews but the one's I really wanted, the 3's, were $179.

I am very happy with the fit, sound and price (even at $70) of these Sennheiser CX300's!

Strength

Overall value/quality/comfort.

Weakness

I would prefer a straight plug vs the 90 degree plug that goes into the iPOD

Summary

I got these in addition to my Grado SR 80 which are unpractically large to use on planes, the gym etc. I absolutely love the Grado's because of their incredible detail.

It is perhaps unfair to compare these Sennheiser in-ear buds to the larger SR 80's, but nevertheless .... they just don't come with the same detail. They're ok for sure, and quite possibly some of the better earbuds out there. However, they don't compare to the rather unbeleivably good sound coming out of the Grado's.

That said, the lower end of the CX 300's is fairly tight and full. And by all means, the sound coming out of these is better than most stereos in the below 5k category. If you don't care about the size of the earphones however, I would dish out the extra dough for the Grado's. If you need something in-ear, these are quite god.

Strength

Surprisingly powerfull bass (beats Grado in this department). Overall good sound.

Weakness

Lack's detail relative to SR 80's.

Summary

Firstly, I paid £32 for these brand new (as opposed to £40 rrp).....not $ =)

These are FANTASTIC headphones.
The sound quality is superb, and they far outclass my other sony mdr-ex71slw 'phones. I have the excellent Sennheiser PX100's which I'll try to compare to.

Sound:
Bass...excellent and deep. Unlike the Sony's however, they don't output overblown baggy bass, it is very tight and tuneful and FAST (Bass starts and stops on a dime with the CX300's). To give an example, various dance tracks that have complex bass-lines tended to come over as a slightly homogenous deep sound only on the Sony's, whereas here they are easily distinguishable from each other...all separated, present and correct.
The Sennheiser PX100's don't reach as deep, but they do tend to vibrate instead...thus giving the impression of deep deep bass (whereas with the CX300's, it's real !)

Midrange...lovely liquid midrange here. Stands out nice and clear, vocals sound like they're physically in your head. Unlike the Sony's, NOT drowned out amongst shrill treble and inaccurate bass.
The midrange is as clear and well proportioned as the PX100's.

Treble...Yes, OK, they do have slightly high treble on first listen, but you need to burn them in first (a week or so of continuos listening should do the trick). When they settle down, they're amazing too. Treble is nicely placed, giving the impression of a nice wide soundstage (to the extent that sounds appear to come from not only inside your head, but also around you sometimes).
The treble in the PX100's is also very clear, giving the impression of nice open soundstage (slightly more expansive too) but the Sony's, conversely, are terrible screechy rubbish.

Build Quality: Exemplary. Better than the PX100's (which are excellent anyway) my silver CX300's aren't simply covered in cheapo silver paint/plastic. It actually looks like metallic car paint with a few coats of piano gloss veneer over it (I was a bit worried that I hadn't opted for the "safe" black ones, but the silvers look great imho).
The material is also very solidly put together. In this respect, you get the impression manipulating them in your fingers of a classy piece of kit.
The Sony's, on the other hand, have appalling build quality using cheap nasty materials.

Comfort: Again top notch. So comfortable that you forget you're wearing them. They're supplied with 3 sizes of rubber "canal-piece" so you have choice like the Sony's. For comfort I'd rate these as high as the Sony's and this also means very little sound leakage.
The PX100's, while good, aren't quite this good and you also get more sound leakage with them

OVERALL
c.f. the PX100's the CX300's sound is very similar with only the soundstage being not as wide and open, but traded off for a much nicer fit with less sound leakage. I would also say that I use the PX100's when I also need ambient sound intrusion (like on a bike), and the CX300's when I don't want to disturb others (on the train).
The Sony's come in a distinct 3rd in all departments apart from comfort.

PS some people have commented that the CX300's are 're-badged' Creative EP630's. This is not true...example CX300 = 18-21kHz, 112dB, asymmetric cord ... but ... EP630 = 6-23kHz, 106dB, symmetrical cord.
Creative just copied the Senny's design is all...they are not the same headphone (different drive units and wiring).

Strength

Accurate, deep and tuneful bass.
Liquid clear midrange.
Nice trable that gives a sense of good soundstage.
Excellent build quality.
VERY comfortable

Weakness

Treble quite high initially, but should improve with a decent burn-in time.
Slightly expensive rrp, but should be able to get at least a third off this online

Customer Service:

Note that the rating is based on the price I paid (approx 80% of the rrp).