Thanks Vulcan! It sounds like the RER/Orlyval option might be the best for me.
My flight arrives at Terminal 1 (United) and I know how to catch the shuttle bus to the RER station.
A question you might be able to answer that I can't find on the official RATP web site...Is the Paris Visite pass available for sale in Paris, or is it one of those you need to purchase here in the States?