Since m2e 1.0 (Maven integration for Eclipse) developers are complaining about issues with the jaxws-maven-plugin.
See here and here.
The m2e wiki offers documentation describing the issue and proposing solutions. For me, none of those suggestions worked.
The classes were not generated and I had to generate the classes using Maven from the command line and refresh the Eclipse workspace. Since upgrading m2e in my Eclipse 3.7 even that doesn't work anymore.
Googling around I found this project hosted on github solving all problems. After downloading and extracting the projects zip file to my computer I installed the connector plugin in Eclipse using the local directory on my computer as update site.
After restarting Eclipse, updating the Maven project configuration and doing a clean rebuild of the project all sources from the WSDL were generated and the project compiled without errors.