Kaz - wholeheartedly recommend either the Shure's or the ety's (Etymotic ER-6i) ... got a pair of ety's myself but have friends with the Shure's and both are fairly similar. Once i bought the ety's I would never think of flying without them!
They're great on noise isolation and it means that you can actually hear the infight movies. I used to have my ipod up at about 80% volume before i bought the ety's and no only need to have it at about 20% for soft listening. At 50% volume, you forget that you're on a plane! When plugged into the IFE, I'm usually only at the first or second volume setting as well. The added benefit is that you're less likely to do damage to your ears if you use the the Shure's or ety's as you don't need so much volume.
I've even compared them back-to-back with the noise cancelling headphones that qantas provide in J class, and they are as good, if not better. The big plus compared to the noise cancelling phones is that the shure's and ety's are so much smaller and much more comfortable when sleeping.
Recommendation on the two prong to one prong adapters... at $5 each, buy a couple if you fly regularly. I've left mine on the plane before ... its easy to do after a long fight late at night! btw, I've never had a problem with them and they work fine in the 3 socket ports as well.