Image S4 is always considered one of the best models for under $100. The newest version apparently is more durable, has a better cable which is flat, and a smaller fit for greater comfort.
I have not experienced them personally, but one competitor to look into would be Etymotic mc5. I can tell you that the Etymotics are great for noise isolation in my experience with the only problem being their microphonics. I mostly solved mine with a shirt clip. I might buy the Klipsch Image S4 and will report my impressions if I do. I lost my Etymotics and it might be time to try something new.
Onkyo TX-NR906S - 360 (GamerTag = Nemo128) - WDTV Live - Logitech Harmony 890 Pro w/ RF Extender
Pana 50PZ850 - Def Tech BP7006 - Def Tech BP1.2x on Wood Tech FBH-36E - Def Tech Mythos Three
Pana 37LZ85 LCD - Onkyo bookshelves