The Cobertura plugin can produce reports in html and xml formats. You can even get both is you want to. Here's how you would configure that:
<project>
...
<reporting>
<plugins>
...
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>cobertura-maven-plugin</artifactId>
<configuration>
<formats>
<format>html</format>
<format>xml</format>
</formats>
</configuration>
</plugin>
</plugins>
</reporting>
</project>