We use the DynDNS.org service for DNS management of some of our hosts behind non-fixed-IP ADSL connections, and had (until now) used the MacOS X-based DNSUpdate client. This client proved a bit too unreliable, and now (thanks to the Unix layer of MacOS X) are using the Perl-based ddclient and cron. Much more reliable!
Should check out No-IP.com, they have a pretty stable mac client. It even uses the Linux client as its daemon and has a nice Mac GUI for configuration.