Paris Digest
Tips on getting from Orly and Charles de Gaulle airports to the city.
http://www.parisdigest.com/transport/charlesdegaulle.htm

ParisBy.com
A map showing public transport connections to the city's two main airports.
http://www.parisby.com/general/frame12b.htm

PIDF.com
Information on getting to and from Paris' airports using a variety of different modes of transport.
http://www.pidf.com/an-world/u_1/home113.asp

RATP
Official source of information on the bus services to Orly and Charles De Gaulle airports.
http://www.ratp.fr/ParisVisite/Eng/index.htm