Any antispam software beside SpamAssassin?

Will all my heart I recommend DSpam. It's more "aggressive" than SpamAssassin, that means false-positives do happen when you start to train it, but I'd rather have to deal with couple of false-positives than a load of spam that did go by unnoticed.

When I was training the filter for the first time, I had to feed it with about 30 spam messsages. After that, each and every unsolicited messages had been recognized properly for more than a year now.

PS. I'd also recommend to use some greylisting software.

ASSP (Anti-Spam SMTP Proxy) is

an Open Source, Perl based, platform-independent transparent SMTP proxy server available at SourceForge.net that leverages numerous methodologies and technologies to both rigidly and adaptively identify e-mail spam.

As of now (June '09) it appears to be under active development.