Marriot to Guests                                                                                                http://www.tampabay.com/news/business/tourism/marriott-maria-shriver-team-up-to-say-please-tip-the-maids/2197857

Discussionfrom Frommers
http://www.frommers.com/community/forum.cfm/tips-tools-deals/lodging/tipping-maid

How to linkfrom About.com.
http://hotels.about.com/od/hotelsecrets/ht/tip_hotel_maid.htm 

Do you tipthe hotel maid? Discussion on Yelp.com
http://www.yelp.com/topic/chicago-do-you-tip-the-hotel-maid      

WallStreet Journal article on tipping the maid.
http://www.nytimes.com/2006/03/07/business/07road.html 

How todiscussion from yahoo Answers.
http://answers.yahoo.com/question/index?qid=20100721090655AA9kD40 

How to fromSuburbanmen.com
http://suburbanmen.com/2012/01/10/how-to-tip-the-maid-properly-at-any-hotel/