Posted at Another Gun Blog:

Back when I was a kid my mom went to the range with a few of the local cops we know. That was her one and only range trip...Mom doesn't know much about what she shot (I've asked) although I do know she shot a DA revolver and that "the trigger was really hard to pull." She also shot an AK-47 and an unknown rifle. We actually have pictures of this somewhere. In one shot you can see her shooting the rifle during recoil with the gun having actually jumped out of her hands. Clearly whatever they had her shoot was not a .22

In my experience, folks unfamiliar with firearms are very nervous on their first outing.  It's a whole lot better to have them come back thinking "hey, that wasn't such a big deal" as to have them come back thinking "that was completely insane."

A .22 semi-auto rifle is a very good place to start for a new shooter.  Ruger, Marlin and Remington all make very nice .22 semi-auto rifles.  This is a bull-barrel Remington 597 with a synthetic stock and a scope:

Once a shooter is thoroughly familiar and comfortable with a .22 rifle, a semi-auto .223 is a pretty good next step up.  AR-15s may look scary on TV, but I've found that new shooters tend to like them in person.  Despite their military looks, AR-15s are user-friendly, ergonomic and easy to handle. 

The Ruger Mini-14 is another good option in .223, and in fact may be a better option for some shooters, given its more "conventional" appearance.  This is the NRA model Mini-14, which is actually a little more "military" looking than the standard model:

Bottom line: please do take your friends to the range with you, but please do use your head.  Start with a .22 and take it from there.  Go at the new shooter's pace.  If you don't have a .22, it's a worthwhile purchase.  I can personally recommend this .22 rifle.

And above all, have fun!