Wikipedia:ISP contact information

Regional WHOIS sources

 * ARIN IPs only. Note: If an IP belongs to an entity outside of the North American region, ARIN will tell you what RIR to consult.

Abuse reporting

 * abuse.net URLs only. Note: If there is nothing in their database, they offer the default postmaster@URL address.


 * spamcop.net URLs and IPs, requires free registration (or use BugMeNot)