For recent releases of Debian and Ubuntu the tomcat6 package includes a dependency on the authbind package and a default authbind configuration that allows the Tomcat 6 container to bind to ports < 1024.
To leverage the authbind configuration edit the Tomcat 6 configuration file /etc/default/tomcat6 and set
AUTHBIND=yes |
See also the man page for authbind.
For example binding to port 443 one would need:
touch /etc/authbind/byport/443 chmod 0755 /etc/authbind/byport/443 chown tomcat6:tomcat6 /etc/authbind/byport/443 |