I don't know if this is a fairly recent addition, but Hampton works in addition to Doubletree.
http://www.topguest.com/programs/hilton
Updated to add: I guess Hampton isn't a recent addition, found this thread
http://www.flyertalk.com/forum/hilto...guest-com.html
Last edited by MarkMColo; Feb 26, 2012 at 2:00 pm
Reason: Update