If you use the Zend Server (CE) PHP distribution on Debian/Ubuntu, apparently there is a conflict between PHP's curl extension and Apache's mod_ssl, resulting in a segmentation fault (crash) upon starting Apache.
The easiest solution is to disable the curl extension, if you don’t need it (by default, this can be done by commenting the first line in /usr/local/zend/etc/ext.d/curl.ini).
Thanks to Sirex for this answer! Unfortunately I am not allowed to upvote his/her answer on StackOverflow yet. I hope this link helps someone else.