At http://checkspammers.xaviermedia.com/ we have a web site where you can check spammers (IP address and email) against several spam databases at once. Since this is posted in the API section of this forum there’s of course also and API available 😉
To use the API just call it from a script like this:
$fspamcheck = file_get_contents('http://checkspammers.xaviermedia.com/check_spammers_plain.php?name='. $name .'&email='. $email .'&ip='. $ip);
This code will return a string with TRUE if there’s a positive match in any of the databases we query. Positive match = spammer
If you use WordPress there’s already a pre-made blog plugin you can use. Just download and install in your WordPress blog.