Web interfaces to SpamAssassin
Generic
webuserprefs [http://sourceforge.net/projects/webuserprefs/] This PHP front-end support web-based administration of both file-based and SQL installations, and a number of authentication options. Detailed configuration directions are [wiki:Self:SingleUserUnixInstall#head-1dd15c06b7e645638def3d2ed2ef31557d853659 available].
For SQL
php-sa-mysql [http://sourceforge.net/projects/php-sa-mysql/]
phpsaadmin [http://www.misak.dk/blog/index.php/archives/category/phpsaadmin/]. There is a demo online at http://www.misak.dk/phpsaadmin/index.php Login with demo/demo
php-sa-mysql2 [http://mail.limelyte.net/downloads/standalone3.0.tgz]. For a Demo of php-sa-mysql2 see http://mail.limelyte.net/webspam/ user test <at> nougen.com, pass test. Notes: php-sa-mysql2 requires register_globals = On, a rewrite is in process.
For Squirrel Mail
There are numerous front ends to Spam Assassin for SquirrelMail, which can all be found at [http://squirrelmail.org/plugins_category.php?category_id=3]
php-sa-mysql-squirrel [http://mail.limelyte.net/downloads/squirrel-plugin.tgz]
user-prefs file generator
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. This only works for SpamAssassin 2.5, not 2.6 or 3.0, and so should now be considered obsolete.