CrunchBang
From LXDE.org
CrunchBang Linux uses the Openbox window manager, with some additional features to make it easier to use. So it already shares the window manager of LXDE.
Simply go to Synaptic Package Manager and search for LXDE.
Or from the command line
sudo aptitude install lxde
An interesting thread concerning LXDE and CrunchBang with some comments from the developer [1]

