After many car-free (and carefree) trips to Sceaux, in October 08 I found myself needing to rent a car. Very limited options in the Antony/Bourg-la-Reine area (none in Sceaux that I could find), and expensive as well.
I ended up renting from Orly airport through Auto Europe. €115 for 2 days for a Citroen C3 (manual, but with a-c). Saved about €65 on what the likes of Avis could offer more locally, so worth any inconvenience.
They actually gave me a VW Touran, which was fine. Probably a free upgrade!
Pick up and drop off (west terminal) was easy, as was getting in and out of the airport. I was worried about the drop off - just before 9am on a Friday - and getting caught up in the rush hour. However, the A86 was nose to tail & stationary going east, but clear going west. I was fine!
Updated Oct 26, 2008
Website: www.autoeurope.com
If Orly is your arrival/departure point, take the Orlyval train service (from either west or south terminals) to RER line B station at Antony. Change there for Bourg-la-Reine, and if you need Sceaux station, change again at B-l-R.
Orlyval only runs between the airport and Antony, so its easy!
Cost for Orlyval is about €7 single (Oct 08) for an 8 minute journey - total rip off. The RER section is extra. The machines will let you include your RER ticket in the one transaction/ticket.
Journey time to B-l-R (the station I use) about 20 minutes, all in.
Quick and easy, but not cheap!
Updated Oct 26, 2008
Website: www.ratp.fr
Best way to get to Sceaux from Charles de Gaulle airport is the RER line B.
It leaves from terminals 1 & 2 at the airport. You have to be careful in the station, as it also serves the TGV line and normal SNCF trains. Always follow the RER signs.
You get tickets from automatic machines, or from a desk in the ticket centre. Again, make sure you go to the RER desk. Queues can be slow moving even if short, as staff deal with people who don't speak French (or English), aren't sure where they're going, and don't know how to get there.
Cost is €20.40 return (Oct 08). The machines take cash or cards, and will offer you an English language option.
Depending on the location of your address in Sceaux, you might go to Sceaux station itself, Parc de Sceaux or Bourg-la-Reine. It takes 50-60 minutes. The service is frequent during tha day - every 8-10 minutes - but less so in the late evening.
The line branches at Bourg-la-Reine, so make sure you take the right train - check the electronic boards on the platforms at CDG. Trains on the Sceaux branch are not so frequent. Heading to the airport, again make sure you get on a train for CDG and not for the other branch.
Line B is plagued by strikes, often at short notice. in that case, often the trains will start/terminate at Gare du Nord so as to cause maximum disruption. If it happens, get a taxi to/ from Gare du Nord - but queues will be hellish! Alternatively, take one of the airport buses to the city centre and then bus/metro/train/taxi from there. The RATP website should announce planned strikes.
Updated Oct 26, 2008
Website: www.ratp.fr
1 - 3 of 3
Reviews and photos of Sceaux attractions posted by real travelers and locals. The best tips for Sceaux sightseeing.

Best way to get to Sceaux from Charles de Gaulle airport is the RER line B. It leaves from terminals 1 & 2 at the airport. You have to be careful in the...
Our members can help!
1

To south of Paris, not far from Orly. Only 20 minutes from city centre on RER. It is like a very small provincial town, which has been swallowed up by the growing city, and has become a very chic...
Build your own Sceaux page