Unless you're willing to shell out for the $300 Bose, I don't think noise-cancelling ones are worth getting. You're much better off with some regular closed-back ones with good isolation. Noise cancelling doesn't work all that well with cheaper sets and it doubles the price for the same sound quality.

I got a pair of Sennheiser HD202s recently (for just $20) and they're great. Only put the volume up to about 30% connected to my laptop, and I couldn't hear the phone ringing even though it was about 3 feet from me. Gonna test them out on a long flight next month, but fairly confident they'll do fine.

If I were to get budget noise-cancelling ones though, the lowest I'd go would probably be the ATH ANC1s.