Personally I couldn't imagine wheeling without a CB. Since virtually everyone I've ever wheeled with has one, you'd miss out on a ton of stuff on the trails. Simply being able to communicate with all the other vehicles you're out with really adds to the experience IMHO, and sometimes it can mean the difference between staying with the group and getting lost.
My first CB was an inexpensive Midland unit from Wal-Mart. I had a 4' fiberglass antenna from Radio Shack mounted to an endcap on the rear bumper. You can read my write-up on it here: http://jeepin.com/features/cb/
I've since upgraded to a Cobra 75WXST which is one of those units where everything is in the handset. I've also replaced the old antenna with a 2' tunable fiberglass whip by K40 that's now mounted on my front fender.
While they're generally not as good as a hard-mounted antenna, you can also use a magnetic mount antenna for general, close-range use (such as on the trail).
One thing that I think a lot of folks don't bother to do, but is very important to do, is making sure you've got a good SWR reading on your antenna. You can pick up an SWR meter for fairly cheap from Radio Shack or some place like that. And make sure you get an antenna that has some method of tuning it (usually this involves lengthening or shortening the tip somehow). Having a good (low) SWR reading means that you're making the most of your broadcasting and reception capabilities so you'll be able to pick up people further away, and that they'll be able to hear you too.
And if you really want to get technical on the installation, you can research ground planes for the antenna and other stuff.