Next version of OSSEC will come with support for PostgreSQL logs and MySQL error/query logs. Since database logging is not something widely done (and even hard to find documentation about), I started in the OSSEC wiki some sections about it. If you are interested in database log analysis, please check out the following pages and help us improve them:
If you have information about logging on other databases (Oracle, MS SQL, etc), send some information to us so we can add support for them on ossec.
*This alpha version of 1.4 has the database support enabled for anyone interested to test: http://www.ossec.net/files/snapshots/ossec-hids-070930.tar.gz