jquery.zebra.js

(function($) {

$.fn.zebra = function(options){
	var default_options = {
		class_name: 'zebra',
		interval: 2
	}
	options = $.extend(default_options, options || {})

	return this.each(function(i){
		if((i + 1) % options.interval == 0)
			$(this).addClass(options.class_name)
	})
}

})(jQuery);