I have been struggling now a bit to find the HAML plugin for Netbeans. All the links I found point to the ‘sunmediacast.com’ website that doesn’t exist anymore, after Oracle took over Sun.
After a bit more googling I found a project on code.google.com where I could download a plugin version. Not sure if it is the latest but it seems to work in Netbeans 6.9.1.
Download it here.