I first bought my cx300's ooh about 2.5 yrs ago, and remeber having had nothing but bad experinces from several ear phones in the past.
These were a pleasant surprise, the fit is very comfortable largely due to them having a sllicone, gel design that just seems to mold around the ear, and the ear canal. They come pre-packed with three different sizes, (I am aware, many of you guys out there are put off this style, of in ear design, due to the fact they may not fit, dont be one of the three will fit just Fine!)

The sound quality is excellent, bass levels are remarkably rich, and mantain high treble levels, and perfect picth with a resounding balance.
Now, most earphone 's under 50 quid, that perform well in bass tests, or say treble underperform in others, its almost like if an earphone will large sound drivers will result in great bass , but at the loss of the clarity in pitch and treble. In short bum, bum, bum, bum of a snare drum may sound great but if you cant't hear the rapsy vocals from Fergies voice (black eyed peas) you not going to be best pleased!
In the sennheiser (German, all the best brands are!) CX300 you have for my money the best earphones around for under £50.
They also look pretty cool, there are better looking earphones out there folks but none that perform better or even as well for the money!
Mark