Description:

Arch's apache package does not currently provide a service for for systemd init.
This would be very useful as it seems Arch is moving to systemd as its default init system.

Additional info:

AFAIK, Apache httpd does not plan to provide a canonical service file any time soon, so I would guess this would be distro's responsibility.
Also AFAIK, Arch packages are mainly moving to maintaining their own service files, rather than rely on something like systemd-arch-units.

An example service file can be found here: https://wiki.archlinux.org/index.php/Systemd/Services#apache2
I imagine it should reside at usr/lib/systemd/system/httpd.service
It seems to be pretty fine.
Some suggestions:
-Possibly apache would want to start after syslog.target;
-And that you could provide the PIDFile=/run/httpd.pid although I think systemd is usually capable of tracking this anyway.
-Systemd can also provide automatic restart, see here for some information: http://patrakov.blogspot.com.au/2011/01/writing-systemd-service-files.html

Gentoo's service file can be found here, as far as I can tell:
http://git.overlays.gentoo.org/gitweb/?p=user/systemd.git;a=blob;f=sys-apps/systemd-units/files/services-server/apache2.service;h=dbc13e0975aa3749f06bae376f1f05a14f6db833;hb=HEAD