define "isolating"
Are you looking for noise ISOLATING (closed back over-the-ear being the most common style) or noise CANCELLING headphones? The difference being the noise cancelling style run an active "cancellation" loop of white noise that cuts out background noise and requires a separate, powered (battery, usually) source.
Everyone's got an opinion and there are a lot of good headphones out there, so I will simply share my experiences. I find that for me (I have sensitive ears) noise CANCELLING headphones flat-out suck. Unless I'm actually on an airplane or in a car (both are rare enough circumstances) listening to music, they clip the sound and muffle/deaden it to a degree I find intrusive. And, the hiss gives me a headache after about an hour or so.
I got my husband a set of Bose QuietComfort 15s on his request for a long flight a few months ago. He based his choice on a quick five minute listen in a crowded Apple store. He used them on a flight, then took them to work, discovered that he doesn't actually like them that much (for many of the same reasons I listed; they kinda suck in a mostly-quiet environment like an office) and I re-sold them to a friend a month or so later.
I got myself a set of V-Moda Crossfade M-100s for the same flight and loved them. They are not 100% closed, but they isolate well enough that background noise on the plane (including crying children, etc.) was reduced to such a degree that I barely had to turn the volume up beyond half on my iPhone to listen to podcasts and music. The sound quality, build quality, style and comfort is impressive on all regards. They don't leak sound despite being semi-open. They don't require batteries (that go dead in 4-5 hours' listening) just to work, as the Bose do. They don't pinch my ears. You can customize them. They aren't muddy at the expense of all other ranges, like the Beats.
My husband stole my V-Modas after we got rid of the QC-15s and I don't use headphones enough at my office to justify getting another set, yet. I'll likely make him buy me another pair before we fly to Europe in a few months.