The JAXB 2.0 RI from Project GlassFish is
That is because it is a very good implementation and the team lead by Kohsuke
has built a strong community contributing to it.
Contributions range from
(like Myungsik Sung from
(like Joost Cassee)
Community building is not cheap, but it pays off!
for a full list of activities he has done in the last couple of years.