要素縦方向のみリサイズ

jquery.resizable.js

(function($) {
	$.fn.resizable = function(options) {
		var default_options = {
			handleClass: "handle"
		};
		options = $.extend(default_options, options || {});
		return this.each(function() {
			addHandle(this, options);
		});
	}
	function addHandle(el, options) {
		var mousedown = false;
		var mousedowny = 0;
		var div = $("<div></div>");
		var r = $(el);
		var rh = r.height();
		div.css("width", r.width());
		div.addClass(options.handleClass);
		r.after(div);
		div.mousedown(function(e) {
			mousedowny = e.pageY;
			mousedown = true;
		});
		$(document).mousemove(function(e) {
			if(mousedown) {
				var diff = e.pageY - mousedowny;
				r.css("height", diff + rh);
			}
		});
		$(document).mouseup(function(e) {
			mousedown = false;
			mousedowny = 0;
			rh = r.height();
		});
		
	}
})(jQuery);

それっぽくは動く