I did some research about this for myself, the best I could find is an advertised -45dB (Remote Audio HN-7506), which makes me very skeptical, I couldn't find any third party measurements but multiple reviews I read mention that they have about the same isolation as Etymotic earphones.
Active noise canceling is good but only for lower frequencies, it does almost nothing to mid and high frequencies, which is not necessarily a bad thing since mid and higher frequencies are easier to attenuate passively.
The best noise canceling headphones have an average noise cancellation of -27dB (-20dB in the bass frequencies), but the best noise cancellation that I could find (other than the HN-7506 that I don't really trust) is from Etymotic earphones, they are completely passive and have an average attenuation of -32dB with -21dB reduction in the bass frequencies which is really impressive, they work so well because they are inserted much deeper in the ear which can be a bit uncomfortable. I read a lot of experiences from musicians and apparently if you use foam tips instead of the stock ones you can get even better isolation and slightly better comfort.
Another option is custom molded IEMs or earplugs, I couldn't find measurements for those but based on comments from people that have them they seem to have slightly less isolation that Etymotic earphones but they're are obviously infinitely more comfortable since they're custom molded to your ears (there are also soft wraps that increase isolation but I don't know how effective they are).
So if you want the best noise cancellation I recommend the Etymotic ER4XR or the Etymotic ER2XR (afaik most Etymotic earphones have the same body (so same isolation), choose them based on the sound signature you prefer), if you want good balance between noise cancellation and comfort get custom molded earplugs or IEMs.
My sources:
Headphones with best ANC measurements, Etymotic measurements (click on Isolation on the sidebar)
I don't know the exact frequencies but it's something I read and noticed myself, and wikipedia seems to agree.
(Don't know what that means.)
Personally I used the Sony XM3 a lot, on planes etc. which have great ANC, and I also used the Moondrop Blessing 3 which are just normal IEMs with no ANC and I only notice a difference in the low frequencies, you can also see that in the rtings measurements (XM3, Blessing 3), isolation in mids and treble is about the same, they seem to consider anything under around 250Hz as bass.