Well, it's been a long time coming but I've finally got my Custom Fields extension built and ready to go for Joomla 1.6+ but it's here now. I've completely re-worked the way that it works compaired to Joomla 1.5.
It's now using proper MVC, the administration is translateable and now to modify the output you use the HTML view override. Here are some screenshots below demonstrating the different custom field administration panels.
This product is still under development and as always please let me know of any major issues, and any fixes or translations are ALWAYS accredited!