From AlphaOmega Software:
You want to display your current IP address in the menu bar? You want to display your user name, your computer name, the IP address, the subnet mask and the MAC address of each of your network interface at the same time? You want your Mac to automatically send an email or upload a file through FTP when one of your IP addresses changes. Then IP Address Menu is what you need. IP Address Menu allows you to display your current IP address (and other information) in the menu bar and to notify you of changes by email or FTP. It displays an icon or your current IP address in the right side of the menu bar. It displays your user name, your computer name, the IP address, the subnet mask and the MAC address of each of your network interface in the menus.
It can display your external IP address (when connected to the Internet through a router). You can copy them to the clipboard by selecting them. It can automatically send an email or upload a file through FTP with all this information and the new IP address when it detects that one of your IP addresses has changed. This can be useful for example if you want to be notified when your remote Mac has changed of IP address because of an internet reconnection. You can configure the subject and the body of the emails sent. You can configure the name and the content of the file uploaded through FTP. It doesn't need any installation which makes it very easy to use. It is available in Danish, Dutch, English, French, German, Hungarian, Italian, Latvian, Polish, Portuguese, Russian, Traditional Chinese and many other languages.