I would recommend the Collett Communicators. I have the older style 900mhz model. We ordered 12 at once, one for all the guys in our group. They cost us about $250 cdn in the end, but they are well worth it. They have 2 channels, one is a general one that all of the communicators come with, and the other is a private "club" channel. Normally the second channel is another general one, but since we ordered as a group, they gave us a free club channel. Also if we order any new communicators, we can have it programmed to the club channel for free.
I must say that thsese things are amazing. They are voice activated, and work really well, when set-up properly. They allow us to keep riding more, and stop less to wait for everyone to catch up. This way, we can realy that someone has broken down, or if everyone is still wit the group. Also it is handy for relaying any trail hazards ahead.
Oh did I mention having music in them also. I have my mini-disc hooked up to the communicator, and absolutely love bieng able to listen to my music while riding down the trail. Then when someone wants to talk, it automatically cuts out the music, allowing for clear communication.
Jeff