Visualforce page to run arbitrary queries on the Force.com REST APIs. See http://blogs.developerforce.com/developer-relations/2013/06/calling-the-force-com-rest-api-from-visualforce-pages-revisited.html for more details.

TestRestApi.page

<apex:page >
  <apex:includeScript value="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-1.7.2.min.js"/>
  <script>
    jQuery(document).ready(function($) {
      $('#queryform').submit(function(){
        $.ajax($('#query').val(),
        {
          beforeSend: function(xhr) {
            xhr.setRequestHeader('Authorization', 'Bearer {!$Api.Session_ID}');
          },
          success: function(response) {
            $('#results').text(JSON.stringify(response, null, '  '));
          },
          error: function(jqXHR, textStatus, errorThrown) {
            alert(jqXHR.status + ': ' + errorThrown);
          }
        });
        return false;
      });
    });
  </script>
  <h1>Test REST API from JavaScript</h1>
  <form id="queryform">
    <input id="query" size="120" value="/services/data/v28.0/query?q=SELECT+Name+FROM+Account+LIMIT+10"/>
    <input type="submit" id="submit" value="Submit" />
  </form>
  <p>Results:</p>
  <pre id="results">
  </pre>
</apex:page>