Two that spring to mind are truncating the DNN Eventlog table regularly, and at the Database level, (if it's suitable,) set the recovery option to simple and ensure that the database log file is set to auto-shrink.

Fairly sure that Mitchel Sellers has some tips on his site at www.mitchelsellers.com too

Barry

Watch out for ANY module that records transactions or logs with any automated frequency.  Banner/advertising modules that track views and clicks and provide methods for rotating content during page views can quickly inflate a table's record count in to the millions - I have seen this myself and remember hearing that it happened to DNNCreative too.  It is no fun to clean up *after* the record count is in the millions, so setup a regularly scheduled cleanup - even if it is manually done.  Of course, don't forget to generate the reports you might need before clearing the data!

Another approach is to run some reports directly on your database.  SQL 2008 makes it pretty easy to get a quick list of each table's size and record count.  There are scripts and tools to do this also and worth looking in to.  Cheers - Jeremy