How to find out what launch agent or daemon is starting a process
You can grep the output of launchctl list for the pid:

$ pgrep -fl foo
40679 bash /tmp/foo
$ launchctl list|grep 40679
40679   -   com.example.foo


Then for example look for a file named com.example.foo.plist in ~/Library/LaunchAgents/, /Library/LaunchAgents/, or /Library/LaunchDaemons/.

Edit: the Disabled key can be overridden in /var/db/launchd.db/com.apple.launchd/overrides.plist, which is modified when launchctl load -w is run as root, or in /var/db/launchd.db/com.apple.launchd.peruser.$UID/overrides.plist, which is modified when launchctl load -w is run as the user.

If the Apache plist that comes with OS X was enabled, you can disable it by running sudo launchctl unload -w /System/Library/LaunchDaemons/org.apache.httpd.plist.