Every time I reinstall my machine and I need to re-download any Vagrant boxes, I always struggle to find pristine images. The ones on vagrantbox.es always have Chef or Puppet or installed, when all I want is an empty Ubuntu machine.
You can find a better box list on the Hashicorp box search
If like me you just want one liners to install them all, here you are:
vagrant box add ubuntu/trusty64 vagrant box add hashicorp/precise64 vagrant box add nrel/CentOS-6.5-x86_64