spamhaus.org ???????????
Google Groups: misc.legal.moderated
The Spamhaus Project - SBL
Use for example "dig +short 0.6.61.69.zen.spamhaus.org", see http://www.spamhaus.org/sbl/latest.lasso for blacklisted IP examples
A good way to find out if a machine/IP is on any lists
Rock tha haus.
Completewhois Multi-RBL Lookup
RBLDNSD
mailpolice
Understanding how RBL's work
RBL's
Openrbl DNSBL RBL Blacklist Lookup
PHPrbl || Realtime blacklisting for your website || rbl for blogs ...
FAQ: POP'ing GMAIL spam - SpamCop Discussion
Resources for Learning and Teaching
The DNSBL countries.nerd.dk