Alas, the death of the wonderful PMX-100's, I just mothballed my second pair, (didn't have the heart to toss them; they'd been through the war so the end of the cord is barely hanging on...but they stil play, just not out on my bike in rough use).
I went on the hunt, and as you found no more PMX 100's, so I went with another pair of PMX - 60, which are pretty good and lightweight.
http://www.amazon.com/Sennheiser-PMX-60 ... rds=pmx+60The best around the neck I have ever heard, and they even blow the PMX-100's right out of the water are the iGrado's,
http://www.amazon.com/Grado-iGrado-Head ... rds=igrado . They actually mounted the drivers from their SR-60's, so they are not even in the same class as the pmx's.
The down side is the drivers are heavier and and amd not be asthetically appealing to some. They are also a bit tight. I find that the fit is uncomfortable after 2 hours on a bike, but they are fine for an hour, so if I'm going out for a while, I use the PMX's.
If you have an isomething, these from Polk are very impressive.
http://www.amazon.com/Polk-Audio-UltraF ... headphonesI had a pair for a day, but the plug on them is made for an iPhone and ahas three connectors, (one for the in line microphone), which made them incompatable with my Sont NetMD. They sounded better than the PMX-100's, but alas I had to send them back.
So I gave up on the hunt to equal my PMX-100's in sound and weight, I went with the good ole reliable PMX-60's.
I've tried a lot of other kinds, but those are the top sport headphones. I had a pair of I think PMX 200's, and I sent them right back, no-where near my 100's.
For home use I have the Grado SR-325i's, they've come down $50 bucks in price but are still $300.00. It's the best sound I've ever experienced.