Taken from:
http://www.linuxsecurity.com/feature_stories/conrad_vixie-3.html

LinuxSecurity.com: Why is nslookup going away? When do you expect this
to happen? Can you give us an example of how to use 'dig' or 'host' as a
substitute?

Paul Vixie: nslookup's functionality will probably return in some form,
since a lot of people seem to like it. The existing BIND8
implementation of nslookup is very closely bound to the internal API of
BIND8, which does not exist in BIND9. Generally, "dig NAME RRTYPE" is
all most people need to know, but if it's important to direct a query to
a particular server then the syntax is "dig NAME RRTYPE @SERVERADDRESS".
Lastly, if what you want is a zone transfer (which nslookup implemented
in its "ls" command), the syntax is "dig NAME axfr @SERVERADDRESS", in
other words, use an RRTYPE of "axfr".

David Conrad: The behavior of nslookup is suboptimal in many areas,
giving weird or un-useful error messages, however it is difficult to
simply fix nslookup as many people rely on the weird behavior
(particularly in scripts). The functionality provided by nslookup will
likely continue (given how many people have written scripts that require
and are used to using nslookup), but we didn't have time to do the full
revision we wanted, so we give a warning suggesting people use dig
instead.