www.velovacations.com - VeloSport - performance oriented trips with some big miles. Usually has Kevin Livingston on some trips.
www.bikestyletours.com - run by Aussie cyclists but caters to Americans more often then not. Has Patrick Jonker some times
www.trektravel.com - Travel arm of Trek & has one or two ex-pro cyclists per week (Kevin Livingston & Jonathan Vaughters) - has high priced Discovery Team behind the scenes trip.
http://www.tourdefrance.com.au/tdf-pas-2005.asp - Phil Anderson's tour group. He is a former pro Aussie cyclist and first non-eurpean to wear the yellow yersey
http://www.stevebauer.com/index2.cfm - Steve Bauer (also former Yellow jersey wearer) runs his own tour company speicalizing in Grand Tours.
these are probably the best that include former Pros - but there are at least 10 other good companies that also run trip to the tour depending on what you want (easy riding, high performance, cultural as well as Tour etc...)