dns-bench.pl is a multi-threaded perl DNS benchmarking tool. I wrote it so I could do performance testing against a DNS cluster at work.
dns-bench.pl --resolver=<host|ip> --targets=FILE [--count=INT] [--recurse] [--progress] \
[--debug] [--threads=INT]
--resolver The dns server to test
--targets A file containing names to resolve, one per line, no comments
--count Number of requests to run [default 10]
--recurse Do recursive lookups [default no]
--threads Number of parallel threads to run to perform the requests [default 1]
--progress Print progress indicator [default no]
--debug Print a LOT of information about what we're doing [default no]