Watch out for the taxi strike scam at Charles de Gaulle airport.
When you arrive at Charles de Gaulle you'll probably be tired from your long flight and possibly a little bewildered as you first set foot into this foreign country. Unfortunately during this somewhat vulnerable moment you may encounter one of the most common scams in Paris: the fake taxi strike scam. Once you've claimed your luggage and pass through customs, you may be approached by a well-dressed man who speaks good English and asks you if you're going to Paris. If you say yes, he'll say, "There's a taxi driver strike today; there are no taxis. I'm a private driver and I can take you to Paris for 100 euros."
Now, fortunately, even though this is a rip-off, the guy really will take you to Paris; he's not going to murder you or anything. But he's lying about the taxi strike, and the price he's charging, 100 euros or whatever, is grossly inflated. On top of that, if you agree to go with this guy, he may try to collect one or two other passengers before you leave, making you wait a bit, and he'll charge them 100 euros as well! With a normal taxi, you're looking at more like 50-70 euros for the whole carload of people. So this is an insane rip-off.
One other thing that I've heard of happening: an acquaintance of mine came to Paris on business with a colleague, the two of them fell for the taxi scam, and the driver charged them 100 euros each! And they were traveling together! This is just crazy. Again, if you're traveling alone or with your whole family, the whole taxi ride should only cost 50-70 euros total.
How to avoid the taxi strike scam?
Easy. Say "no merci" to the guys who approach you in the airport. Follow the signs for taxis; you can't miss 'em. When you get to the taxi area, an airport employee will be there to assign a taxi to you. There may be a line; just wait, it moves fast. Once you're in your taxi you'll be just fine. I personally have never heard of anyone getting ripped off by the legit taxi drivers at CDG airport.
There's no flat fee from the airport, so the driver will turn on the meter and you'll pay depending on how far you're going. There may be an additional fee for baggage; something like one euro per bag, and this should be posted in the taxi on a window decal or something. The first time a driver charged me the baggage fee I suspected it was a minor scam, but I'd merely missed the sign. It's legit.
I would say it's normal to tip your driver around 10%, but this is a hot topic of debate among my Parisian acquaintances. I always to try to keep a five-euro bill handy for longer trips like this, and honestly this may be overdoing it. Please see my article on tipping in Paris for more info.
Uh, sometimes there really is a taxi strike.
You may arrive at the taxi area ouside the airport and learn that there really is a strike. This is rare, but it can happen. In that case, you can either go with one of the private drivers, or take the RER (regional train) — much cheaper, but pretty unpleasant with a lot of luggage, as there are a lot of stairs and escalators to deal with. See my article about taking the RER here.
Again, the private drivers will definitely overcharge you, but hey, they'll get you where you're going, and at least they're not lying to you (this time).
Good luck, safe travels,