Anything else you're looking for in a pair of headphones? Budget? Music/sound preferences? What kind of noisy places would you take these headphones to? How important is comfort or durability to you?
In-ear headphones can have better passive noise isolation than the best noise-canceling headphones (like the QC15), since they basically double as earplugs in function. Be careful, though, as some of them do it so well that you wouldn't be able to hear a car before it runs you over, among other possible hazards.
For absolute isolation, a well sealing pair of iems is the way to go. The original Etymotic ER-4p and 4s used to be one of the best, though there are many options these days. If you need even more, some ear protection muffs on top of the iems will chop out noise even more. You can even get active noise cancelling muffs.
For noise cancelling headphones, bang for the buck the Audio Technica ANC7b is my top pick.
For passive cancellation: Sennheiser HD280/380, HD25-1, Beyerdynamic DT770