Blacklist

MultiRBL.valli.org - Blacklist, Whitelist and FCrDNS check tool

http://multirbl.valli.org/lookup/ search multiple DNSNL

Flow Control 2.0 — IP Reputation Tool - Sendmail.com

http://sendmail.com/sm/resources/tools/ip_reputation/ IP-reputation tools from Sendmail.com (spam-score of an IP address )

Email Blacklist Check - See if your server is blacklisted

http://www.mxtoolbox.com/blacklists.aspx website that does blacklist lookups.