As already mentioned
http://www.greathobbies.com
and also,
http://www.hobbywholesale.com/
both have a good selection but cannot match Tower Hobbies for overall stock but they both do a pretty good job of having lots available.
and, if you into electrics try
http://www.zebrahobby.com/ good selection and great service.
cheers, Graham in Embrun near Ottawa Canada