Statistics and log analyzers
These are tools to analyze SpamAssassin logs and generate reports. Generally, they take syslog data logged by the 'spamd' server as input.
qmailmrtg [http://www.inter7.com/mrtg.html] - example output: [http://www.sk-branik.si/qmailmrtg]
vispan [http://www.while.homeunix.net/mailstats/] - demo: [http://hosting.boys-brigade.org.uk/mrtg]
mailwatch [http://mailwatch.sourceforge.net/] - no demo, but the previous link has screenshots
mailscanner-mrtg [http://mailscannermrtg.sourceforge.net/mailscanner-mrtg/] demo: [http://mailscannermrtg.sourceforge.net/mailscanner-mrtg/]
logreport.org apparently has a syslog analyzer that can grok spamassassin logs: [http://logreport.org/lire/or/email.php]
sa-exim-stats [http://nossie.addicts.nl/projects/sa-exim-stats/] : Generates rrdtool graphs from sa-exim log files.
mailgraph [http://people.ee.ethz.ch/~dws/software/mailgraph/]: Generates graphs from syslogs. demo: [http://people.ee.ethz.ch/~dws/mailgraph/mailgraph.cgi]
monkeynoodle.org spamassassin MRTG scripts [http://www.monkeynoodle.org/comp/tools/spam]: Scans the maillog/syslog and feeds the SA results into a format from which MRTG is used to create graphs. demo: [http://www.monkeynoodle.org/mrtg/felix.html]
spamdstats [http://www.ini.ethz.ch/~stephan/software/spamdstats.tar.bz2]: Continuously parses spamd's log file in the background and stores various data in one berkely db file to be read by a second script.
If you plan to parse spamd's syslog output, some helpful notes can be found at SpamdSyslogFormat.