When trying to change a page layout, was seeing nothing.
Using browser developer tools I was seeing a javascript error, which with a bit of searching led me to this article: http://johnliu.net/blog/2010/12/22/sharepoint-2010-quick-fix-for-ribbon-page-layout-switch-java.html which solved the problem.
(Basically there are page layouts that are broken and cause the drop down not to display, removing non-used layouts fixes the problem).