I just got my battery-powered bike intercom from JC Whitney. It cost about $60 with shipping, and the wife and I are trying to work the bugs out. Sounds great at low speeds, but she likes riding with the visor up, so I need to tweek her mic position and put on the wind-covers because of the wind noise generated. She says she hears me fine (my helmet was easier to thread the mic boom to front of shell). It's the IC993 model... nothing much to it, just 2 helmet headsets with cables, and intercom unit (about size of a wallet) which clips easily to the velcro straps at the bottom of my riding jacket.
It has a volume control, and an additional audio jack for radio or whatever, which is overridden when you use your mic to talk. Link to Catalog