What is te CommandUIDefinition Location for adding a button to the Page Actions section of a publishing page? I looked on this page but I could only find Web Part Pages and Wiki Pages.
One of those is what you want I think, if you view source on a normal publishing page you can see IDs like :-
even though it isn't a wiki page...
I am fairly sure that in C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\14\TEMPLATE\GLOBAL\XML\CMDUI.XML you should be looking at:-
<Tab Id="Ribbon.WikiPageTab" Sequence="1000" Command="WikiPageTab" Description="" Title="$Resources:core,TabWikiPageTitle;">
The Title attribute of that node refers to a resource file value which in English is "Page"