example.js

$('.zipcode').whitelist(/\d/);
$('.state').whitelist(/[A-Z]/);
$('.plain').blacklist(/[!.,<>();:-_]/);

whitelist.js

(function($) {

function in_list(e, expr) {
  return e.charCode > 0 
      && String.fromCharCode(e.which).match(expr);
}

$.fn.whitelist = function(expr) {
  return this.keypress(function(e) {
    if(!in_list(e, expr)) e.preventDefault();
  });
}

$.fn.blacklist = function(expr) {
  return this.keypress(function(e) {
    if(in_list(e, expr)) e.preventDefault();
  });
}

})(jQuery);