ARIN: American Registry for Internet Numbers: <http://www.arin.net/>.

Sample queries:

  whois -h whois.arin.net 66.94.230.41

  	Will tell you to whom the IP address is assigned.


  whois -h whois.arin.net '?'

  	Will return help information.



General form and options:

  whois -h whois.arin.net <query string>

  flags to limit search by record type:

    n	network address space
    a	autonomous systems
    p	points of contact
    o	organizations
    c	end-user customers

  flags to query by attribute:

    @<domainname>	search for matches by the domain-portion
    !<handle>		search by handle or id
    .name		search by name

  wildcard:

    Append '*' to a query to match trailing characters.

  flags to control display format:

    +	full output
    -	summary output
    <	Show parent networks in detailed format.
    >	Show subnetworks in detailed format.

    Default is full output if there's only one match, else summary.


More information, and a full tutorial can be found at
http://www.arin.net/education/WHOIS_CBT/index.html