Yaesu - for leading the tours, I have three actually. We have a Chatterbox X1 that my videographer uses. Trick is the battery only lasts one day, so by 6pm, his battery is dead. Plus we couldn't get the cheapy handlebar-mounted-push-to-talk to work very well, and the VOX sucks. Trick was for him to reach up with his left hand (in the straights of course) and hit the push to talk button on side of his helmet. That worked great, and we could converse all day. You can hardwire it.
I have been using the AutoCom for last two years, about $500 for that setup, my partner uses a more fancy version with all the hookups- about $700, uses normal military grade walkie-talkie (cheapy one would work), and the basic Autocom unit. All hardwired into the Hayabusa, push to talk on handlebar. Microphone is flawless on that, and me & my other tour guide can chat all day at moderate speeds. Need line of sight though to get good reception. Once we're in the twisties, or say 1/2 mile away, no worky.
I just got the StarCom1 Advance System,
LINKY from CA Sport-Touring, starts at $280 (remember, you still have to buy the walkie-talky) whole sheebang, Handlebar mounted push-to-talk, cell phone hookup (I haven't told my wife about that
), CD (iPod) hookup, hardwired into bike, hard mounted inside the tail and all wired through the busa.
I have ridden with guys that had the Baehr system (BMW dealer is pushing that one), we're talking pretty expensive, easily get up to $1000 with all the bells & whistles.
Nice thing about the Chatterbox is it's good entry level system and has the transmitter built in. I spent almost $400 for Chatterbox X1 with all the hookups. All these systems are using the same signal and are compatible to talk.