I got a set of TripleFi 10's off of craigslist this past Thursday and I am blown away by their sound quality. I researched quite a bit, and most of my research pointed me to these forums and by looking through the files here, it seemed to me that these headphones are pretty much the best bang for the buck (about $100) out there.
My previous, good high quality, headphones were the Etymotic ER6i which I bought in HK back in '05(?). They recently started to short out at the base of the cable from repeated gym use, so I deemed a replacement set was necessary. I also have the B&O headset which produces great sound quality but no bass and aren't the most comfortable around.
But these TripleFi's are amazing, probably a bit too good for my library, because it seems that I have a lot of music that wasn't encoded in lossless and I can hear the distortion that would otherwise not be audible in lower quality headphones. But all in all, my music sounds completely different, tracks like "Empire State of Mind" just sound like 2 different songs when comparing the TripleFi's with my old ER6's let alone stock iPhone buds.
I do have some issues with the silicone tips, for some reason I can't get a long lasting seal on the left side, but the memory foam ones work perfect, and I ordered some extra Tx-500's.
Oh yeah, and I got a set of SuperFi 4vi for the gym so I don't break my good headphones. $25 on eBay, they may be knockoffs, but I doubt it because they sound quite good. At that price for iPhone compatible sound isolating headphones, I may pick up a couple more sets.