Sennheiser Adidas CX 680i Sports Headset

This really is a great set of in-ear sport earphones. The noise cancelation is really good, I used it while biking and on public transportation too - had no issue with outside noise. The build quality could be a little bit better, but the lightweight plastic construction is needed so they are lightweight. The fake kevlar-looking insert on them fells off pretty soon (I had two sets of these earphones, that plastic piece lasted a year each time) In my opinion the symmetrical cord wasn't the best choice as an asymmetrical one would be a lot more comfortable and would offer a better fit and not getting tangled while running.
 
As it was mentioned before me, the comfort is great, the fins keep the earphones in your ears and I don't think sweat could be an issue for anyone. Sound quality is good, detailed mids, bass is good.
Came with a carrying pouch and a set of S/M/L sized fins, no-fin rubber parts, sponges for the canal (to soak up sweat), a tool for swapping the sponge and buds.

I bought this pair of headset from Amazon earlier this year. The sound quality is very impressive just as advertised (energetic sounding). After a few months of use, the headphone began to fall apart. First was the rounded rubber. Then the plastic part broke, which can be quite annoying sometimes. Due to those two failures, I had a hard time keeping them in my ear during running workouts. 
 
Overall, I am satisfied with the headset. I would recommend this pair to my friends.

I lift weights, i dont run with these, i dont play basketball with these, i sometimes skateboard with these. Keep this in mind.
 
 
Audio quality is great, blocks all other sounds out, and keeps my music in. I cannot hear anyone at my gym, no grunts, no weights dropping, no bad gym music. I love this fact, i can zone in way better. Bass is a little lacking, but cant expect too much from these.  Music sounds bets when tight in the ear and has a tight seal.
 
The headphones to the 3.5mm jack is about 2 feet, way too short to reach from your ears to your ipod in your pocket. But would work if you used an arm band.  And you wont have on-cable volume control.
 
Whats included is a 3.5mm in -> volume control -> 2 ft cable -> 3.5mm out. You would attach the headphone part to these and extend the length of the cable . This works well, the volume knob needs some force which is what you need so the music doesnt fly up or down by accident.  The headphone 3.5mm plugs in VERY securely and will not randomly slip out.   The downside is the awkward length between the headphones and the volume control knob.  Its not a dealbreaker by anymeans, its just my only real gripe.
 
The fins are made out of soft rubber and fit nicely, comes with bigger, smaller and a no-fin part. Also the in-ear yellow rubber part also comes with larger and smaller sizes. I found the standard fin with larger yellow buds fit the best for me.
 
Also comes with an awesome holding bag, has Adidas sign on one side, and says sennheiser on the other.  Fits my 160gb ipod with a case and these headphones perfectly. (size reference)
 
 
100% worth the 30 dollars i paid.    (check ioffer.com thats where i got mine   )
 
I will add a pic and am available for questions, just shoot a PM or post right here.