QUOTE(Dias @ Mar 31 2008, 07:18)

My CX300 has gone today (only R speaker still works...) and I need for a quick replacement since I use headphones a lot. What alternatives are there (same/better)?
Any reason why you're not just picking up another pair of CX300s?
QUOTE(JunkieXL @ Mar 31 2008, 11:32)

I've used the CX-300 and own a pair of CX-500's.
I can highly recommend the CX-500's. They have a slightly better sound than the 300's. The sound is a little more detailed and crisp and it still has some great bass output.
I wouldn't recommend running in these though.
Get a pair of the street style type headphones that wrap around the neck. I've used IEM's, ear buds and the street styles while running and the street style always worked best.
Sennheiser PMX-100 linkage There are few more choices to choose from on the website I've linked to as well. I've also heard that the Koss Porta Pro's are good for their price, but I just don't like their styling and am not a big fan of the company.
JXL
I agree with you about the CX-500s... but the original poster was shopping to a $50 price point. The headphones I'd buy for runnings are the Sennheiser PMX70 Sport, but again, the original poster wanted canal phones. (When I jog, I'm use a mediocre pair of Philips/Nike headphones... but after briefly borrowing a pair of the PMX70, I'm ready to upgrade).
My primary pair of headphones are the Sennheiser PX100. I've yet to find a better balance of sound quality and price.