To name a few:
- Translators have got an openSUSE 10.3 retail box and an openSUSE t-shirt;
- Packagers, those who joint the Packaging Day, got openSUSE t-shirts, baseball-hats, and even tuxs.
In my opinion this is an awesome openSUSE/Novell initiative to raise up some (healthy) competition between the people already involved on the project and people who never thought that contributing to an open source project could have had any returns for helping the project itself.
Even though if you don't know how to package or translate openSUSE into your language, or even if you don't want to do these things you can do something you like/want to help the project - eg: promoting openSUSE (events, blogging, LPIs), bug reporting, helping people on web forums, and IRC, writing articles on the openSUSE wiki, etc...
As always, Novell and the openSUSE team will give you full support, providing you anything you need to execute your volunteering task - at least, they did it for me ;-)