pgeodns is a simple DNS server that can distribute load for a hostname to the nearest mirrors (as defined by geography; on the country / continent level).
It is used for search.cpan.org/cpansearch.perl.org and for ftp.perl.org/ftp.cpan.org. It is also used to provide nearby-ish servers for the NTP Pool.
It's not quite as feature rich as we would like, but it gets the job done. (And hey, it's not much code so you can probably hack in whatever you need). :-)
For our use we only need a few hundred DNS lookups per second per DNS server, so we don't know how well it scales. (But on modern hardware the answer is likely "well enough for what you need").
The latest release can be downloaded from the downloads page. The git repository is at at git.develooper.com and github.
We have an issue tracker on google code and a mailing list. We also have an ohloh page. :-)
Email ask@develooper.com with questions, comments and patches.
pgeodns is copyright 2001-2009 Ask Bjørn Hansen, Develooper LLC and licensed under the Apache License 2.0.