TWIG
I would recommend using Twig 
- extensible syntax
 
- efficient
 
- compiles and caches your templates to PHP classes with a very small overhead
 
- sandbox mode to evaluate untrusted template code
 
- unit tested
 
- great documentation
 
- multiple template inheritance, template blocks, automatic output-escaping
 
Also read Fabien Potencier's blog post, where he explains needs for a powerful and customizable template engine.
TWIG Template code
{% extends "layout.html" %}
{% block title %}
    {{ page.title|escape|title }}
{% endblock %}
{% block content %}
    Content of the page...
    {% for user in users %}
      * {{ user.name }}
    {% else %}
        No user has been found.
    {% endfor %}
{% endblock %}
{# this is a comment in twig syntax #}
Symfony Components
Also if you need additional components for web development, but you already have a defined code base, have look at Symfony Components which includes additional templating component (mentioned in XUE Can answer)