Update March 13, 2012: The report at ziembor.pl is no longer available (and not working on OpsMgr 2007 R2 and later anyway). Updated in the Logical Disk Extension MP at http://www.systemcentercentral.com/Downloads/DownloadsDetails/tabid/144/IndexID/64216/Default.aspx
from http://ziembor.pl, this Logical Free Disk Space report improves on the out-of-the box options in OpsMgr. Both the sql source code and an MP in which the report is delivered can be downloaded from the authors site.
Click the link at right to go to the authors site.