Noise Canceling
dB ratings are claims by manufacturers. I haven't found an independent test yet.
Bose
Panasonic
300g 18 dB $200
150g 12 dB $100
Shure:
ear buds 37 dB

NY Times David Pogue June 14, 2007
The "active noise reduction" technology used by these headphones generally cancels only lower frequencies. Higher ones are difficult to stifle electronically. Whatever upper-register noise cancellation you get from these headphones, therefore, comes from the seal they make with your ears, which is "passive noise reduction."
Not as good as Bose but very good for the price. All but the highest frequencies are subtracted.
Audio-Technica ATH-ANC7 $132
Audio-Technica ATH-ANCI in-ear
Sony MDR-NC500D 14dB $400
Panasonic RP-HC500 $100
Bluetooth: