[Ryolith]

I've upgraded from skullcandy inkd ($10) to JVC fxt90 ($140) recently.  No monitor in between.  The difference is very obvious.

 

[KimChee]

Yeah you can tell the difference.  My first big jump was to RE0, I was impressed.

 

[Axesd]

I actually like the Shure SE215

 

[Alexus]

 
Let me tell you my short story. I used to have Apple's earphones for years. Then I decided to buy something new and I've got Sennheiser CX980 ($200). I was really shocked and impressed. Then I thought to myself if $200 iems are so good (and better then Apple's) then what will I get from $500 iems.  
 
After one week of having CX980 I bought Sony MDR-EX1000 ($450). And their sound was more like Apple's earphones rather than Sennheiser. CX980 had so much bass and Sony's iems were not so bass-heavy. But after my first quiet night with EX1000 I was much more impressed than before. Now I can't listen to "boom" sound of CX980 (or flat and dull sound of Apple's earphones) and I enjoy so much this crystal clear sound of EX1000. Jazz and Classical music become so wonderful... Also the voice sounds so real and good on EX1000 (when I compare it to Apple's I feel like singer sing through the cloth, like there is a veil between singer and me). 
 
And when you get expensive iems you will get the new dimension of music. If before you heard instruments with your cheap eim now you will also hear the distance between those instruments. Voice is separated from instruments, everything sounds just so right and good. And you can hear that guitar is left to you and piano is left to you too but a little futher then guitar etc.
 
Now I have EX1000 for a week and very glad I bought this iems. But it really takes some time to "understand" and get used to it (after boom bass or very "colored" sound). But it worth it! And now I'm looking to get a new rig for home based on fullsize cans (I listen to music only at home, because it's not safe to use headphones in the car )

 

[killmurer]

When I went from the S4 to the SR-60i s I could easily notice the difference. Not just sound signature wise, sound quality wise too. Grado was so much better to my ears. Instrument separation, sub bass mid bass, highs, lows, it all makes sense. Just you wait