Ipanema will keep track of the IP addresses for ethernet, Airport, PPP, and a 3rd party ethernet card (if installed) and report to you the IP address automatically via OS X Mail once a day. You can also manually send a report of the addresses anytime you wish. If an IP changes, it will automatically send you a report of what has changed. Ipanema also displays your "real" IP address if you are behind a firewall.
What's new in Ipanema
Version 1.3 adds the following:
New graphics & interface changes
Ability to shut off external IP checking
Ability to specify when Ipanema checks for changes