I've done a bit of research into the muffs available. None are "Noise Cancelling". Noise cancelling requires some consistency to the noise so the electronics can generate a counter sound wave. The electronic muffs I've seen have a microphone so you can carry on a conversation, but when a loud noise happens, the microphone cuts off so the speakers don't blow your ears out.
There are many good electronic muffs out there. I've used the $13 cheapies from Harbor Freight to some pretty nice Peltor's. They all seem to work. Look for something that has a high DB reduction (30 DB or more if possible), provides a good seal around the ears and are comfortable to wear. Don't really recommend the Harbor freight models, nothing really wrong, but the batteries are under the foam that cushions your ears. Hard to change batteries and sometimes they just don't stay together. I like the Peltor. Comfortable, good sound quality, good sound reduction, and just nice muffs.
Peltor brand is a 3M product if I remember, and is available at Walmart. Not too pricey, plus have a 3.5mm jack so you can plug in a MP3 player if so inclined. I paid $50 or so for my Peltor's and really like them. Peltor muffs can get pretty expensive so look for the features you want.