Ok, I finally know what the problem was. I did yum install mod_ssl for testing purposes on the old server. Again httpd was not able to start again!
Also I have to say to that people that also consider lighttpd: be sure you will be able to configure it, mod_expires is less configureable and sadly enough the errordocument handling is very bad. But we also have the advantages of chroot and other configuration options :-)
Anyways. If you encounter problems with your apache (without errors), first try to disable the modules one by one and see if it comes up ;-)