Web interfaces to SpamAssassin
php-sa-mysql [http://www.peregrinehw.com/downloads/SpamAssassin/old/php-sa-mysql-0.5.tar.gz]
phpsaadmin [http://www.aub.dk/~misak/]
webuserprefs [http://webuserprefs.pipegrep.net/]
Michael Moncur's spamconfig.php: [http://www.yrex.com/spam/spamconfig.php]. This generates a file suitable for download, rather than being a UI you can install on your server directly.