Q:

Print login page url in node.tpl.php

It seems nevertheless rather simple, but I do not find the solution. 
How to print in node.tpl.php the url of the login page? 
The url has to serve for a link:
<a href="<?php print ... ?>"><span>Login</span></a>

A:

Use this if you just want the URL:
<?php print url('user/login'); ?>

If you want to print a link:
<?php print l(t('Login'), 'user/login'); ?>

And in your case it would be:
<?php print l('<span>' . t('Login') . '</span>', 'user/login', array('html' => TRUE)); ?>

