As a public service, McFadden Associates maintains a free DNSBL blacklist. Anyone sending SPAM into their mail filters is automatically added for a period of thirty days.

Weekly reports of DNS blacklists lookups of IP addresses (and reverse DNS lookups) that made SMTP connections to the San Diego Supercomputer Center on that week. Useful for getting a grasp of the size of the various blacklists. Maintained by Jeff Makey.

Provides reports on whether there is recent spam activity within each IP block, especially spamvertised web site addresses. Check if you are sharing your address block with spammers.

Lists IP blocks of China and Korea for those who want to avoid asian spam.

The CBL is a DNSBL which takes its source data from very large spamtraps, and lists IPs of open proxies and worms/viruses.

Lists all DNSbl's (RBL's) and enables users to make a query against all the lists.

A manually updated and verified online database of spammers. Provides email address and domain blocklist.

Blacklist that includes dialup equivalent ip addresses, individual spam sources, netblocks that refuse to remove spammers, bulk mailers that don't require confirmed opt-in, output servers from multi-stage open relay chains and single stage open relays...

A realtime URI blacklist served via DNS to identify unsolicited bulk and commercial messages based on the links within the e-mails. Distributed under the Apache open source license.

MAPS aims to defend the Internet from spammers by educating ISPs and providing real time blocking lists of known spam sources.