I'm not sure what is the best/recommended way of finding JBDS nightly builds, but I went to https://jenkins.mw.lab.eng.bos.redhat.com/hudson/view/DevStudio/view/DevStudio_Master/job/devstudio.product_master/ which has a link to http://download.jboss.org/jbosstools/builds/cascade/ which redirects to http://download.jboss.org/jbosstools/builds/cascade/master.html and there is this link there:
http://www.qa.jboss.com/binaries/RHDS/builds/staging/devstudio.product_Master/installer/
The correct link is:
http://www.qa.jboss.com/binaries/RHDS/builds/staging/devstudio.product_master/installer/ (see the lowercase "m" in master)
Also, the cascade page says this at the top which is wrong:
JBoss Tools 4.2.x / JBoss Developer Studio 8.x (Kepler) [master]
Should be luna.