gistfile1.txt

      var combo = new Ext.form.ComboBox({
        xtype: 'combo',
        name : 'perpage',
        width: 40,
        listWidth: 40,
        store: new Ext.data.ArrayStore({
          fields: ['id'],
          data  : [
            ['15'], 
            ['25'],
            ['50'],
            ['100'],
            ['500']
          ]
        }),
        mode: 'local',
        value: '15',

        triggerAction : 'all',
        displayField  : 'id',
        valueField    : 'id',
        editable      : false,
        forceSelection: true
      });