Underscore.template: Super-simple/-stupid partials. It's quick and dirty yet it does what I want, so there.

example.js

// Fetch the template HTML from the DOM, hand it over to `Underscore.template`,
// assign some variables, and set up a `partial` method.
var template = $("#tmpl-main-section").html(),
  compiledTemplate = _.template( template, {
    models: aCollectionOfThings,

    // See template examples below on usage.  It's all very complex.
    partial: function( partialName, variables ) {
      return _.template(
        $( "#tmpl-" + partialName ).html(),
        variables
      );
    }
  });

// Append the compiled template to the document body.
$("body").append(compiledTemplate);

templates.html

<script type="text/html" id="tmpl-main-section">
  This is my main template.
  <%= partial( "my-partial", { descriptor: "ossum partial" } ) %>  
</script>


<script type="text/html" id="tmpl-my-partial">
  This is my <%= descriptor %>.
</script>