Couple schools of thought on this one, and sure many folks will chime in. Here are a couple options i see:
1. J&M CB2003: CB radio, intercom, and audio port that can connect to almost whatever you can mount on the handlebars that "talks" (ie a GPS).
2. Smart phone: I personally use an Iphone 4 with a Scala G4 bluetooth helmet comms system. I can make calls, listen to police scanner, radio, music stored locally, receive calls...I just keep my phone in my pocket or tank bag and away I go. Some people actually put a RAM mount on their handlebars and slide the phone in a cradle on the RAM, most likely for GPS applications. I personally don't do this and prefer a separate GPS unit. To each his own, and gotta find what works best for you.
3. Some of the Garmin units also have blue tooth and MP3 capability, and interface with your smart phone for making calls. Haven't seen one with a built in CB though.
4. other systems: someone else is gonna have to fill in the blanks here...