I'm not really a fan of template engines that force you to use another "language" to put your data into the templates (ie Smarty, TemplateLite, phpBB template class, etc). It seems to me that PHP is a template engine in and of itself and there's really no reason to use something else entirely to render your markup.
Something I have used in the past that, to me, is the cleanest way of doing it, is
the Savant templating package. This particular package is essentially the view layer used in the Solar Framework by Paul M. Jones. It is clean, fast, and all PHP. If you are planning on separating your views out I'd recommend something like this.