Personally I preffered Kerr's 150/2 model from Scottish Central, however MT have released their Class 150 stock pack. The base pack includes 2 units and an activity, and there are 6 further free "expansions", one of which has already been released.
http://www.makingtracks-online.co.uk/index.php?option=com_content&task=view&id=367&Itemid=1
http://www.makingtracks-online.co.uk/index.php?option=com_content&task=view&id=367&Itemid=1