Yeah I've looked at some noise cancelling mics but they are usually pricey and my goal is to blanket my whole house with mics so you can control my system from anywhere.
Usually "noise cancelling" mics work by direction & proximity... A headset mic with your lips right-up to the mic. It won't help in your application. I believe they were invented for airplane pilots. Or, there may be some electroinic noise-canceling mics that work like a [u]noise gate[/u] (also not useful in your application).
Directional mics (cardiod, super cardiod, and shotgun) can give you a better signal-to-noise ratio but it's only going to help you under certain marginal conditions. And, they typically start at around $100 USD.