MochiKit.Cookie or MochiKit.Storage

these are in my tool box. I'm commenting to ensure you consider the case of not enough memory for setting the cookie, which can cause bad rendering of overloaded pages.

function setCookie(name, value, expires, path, domain, secure) {   
    var val = escape(value);
    if (document.cookie.length + val.length < MAX_COOKIE_SIZE) {
	throw new MochiKit.Base.NamedError("MochiKit.Cookies.NoMemory")
    }
    document.cookie= name + "=" + val +
	((expires) ? "; expires=" + expires.toGMTString() : "") +
	((path) ? "; path=" + path : "") +
	((domain) ? "; domain=" + domain : "") +
	((secure) ? "; secure" : "");
}

function getCookie(name) {
    	var dc = document.cookie;
    	var prefix = name + "=";
    	var begin = dc.indexOf("; " + prefix);
    	if (begin == -1) {
        	begin = dc.indexOf(prefix);
        	if (begin != 0) return null;
    	} else {
        	begin += 2;
    	}
    	var end = document.cookie.indexOf(";", begin);
    	if (end == -1) {
        	end = dc.length;
    	}
    	return unescape(dc.substring(begin + prefix.length, end));
}