We use something called a "scala cardo" which is aimed at motorcycle, but works fine adapted for bicycle helmets. It is bluetooth technology and pretty idiot proof I'd guess, though sometimes seems to have issues "pairing up" they are always resolved quickly, sometimes without any intervention on our part.
Was a little pricey I think around the £130 mark. Seems to give very good battery life, small and light and survived a few really wet rides, so no issues with weatherproofing either.
Something I might look for in future though is ability to play music or radio through the system without wires (there is a socket for a mini jack, but I believe that will playback only through the one headset). Then again that is a whole new kettle of fish and stoker will likely want me totally listening to the road, traffic, and her sweet self!