Just for reference… here are some searches extracted from the Deployment Monitor application (only slightly modified) and other useful ones. I know there are apps for this, obviously DM that I extracted some searches from. But who knows, sometimes these apps may not work.
The great ppl @ Splunk have also documented these searches and more:
http://www.splunk.com/wiki/Community:TroubleshootingIndexedDataVolume
http://www.splunk.com/wiki/Deploy:Splunk_Metric_Reports
Usage by source: