Of course slideDown and slideUp don't do what you want, you said you want it to be left/right, not top/down.
If your edit to your question adding the jquery-ui tag means you're using jQuery UI, I'd go with nnnnnn's solution, using jQuery UI's slide effect.
If not:
Assuming the menu starts out visible (edit: oops, I see that isn't a valid assumption; see note below), if you want it to slide out to the left and then later slide back in from the left, you could do this: Live Example | Live Source
$(document).ready(function() {
// Hide menu once we know its width
$('#showmenu').click(function() {
var $menu = $('.menu');
if ($menu.is(':visible')) {
// Slide away
$menu.animate({left: -($menu.outerWidth() + 10)}, function() {
$menu.hide();
});
}
else {
// Slide in
$menu.show().animate({left: 0});
}
});
});
You'll need to put position: relative on the menu element.
Note that I replaced your toggle with click, because that form of toggle was removed from jQuery.
If you want the menu to start out hidden, you can adjust the above. You want to know the element's width, basically, when putting it off-page.
This version doesn't care whether the menu is initially-visible or not: Live Copy | Live Source
<!DOCTYPE html>
<html>
<head>
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.10.1/jquery.min.js"></script>
<meta charset=utf-8 />
<title>JS Bin</title>
</head>
<body>
<div id="showmenu">Click Here</div>
<div class="menu" style="display: none; position: relative;"><ul><li>Button1</li><li>Button2</li><li>Button3</li></ul></div>
<script>
$(document).ready(function() {
var first = true;
// Hide menu once we know its width
$('#showmenu').click(function() {
var $menu = $('.menu');
if ($menu.is(':visible')) {
// Slide away
$menu.animate({left: -($menu.outerWidth() + 10)}, function() {
$menu.hide();
});
}
else {
// Slide in
$menu.show().css("left", -($menu.outerWidth() + 10)).animate({left: 0});
}
});
});
</script>
</body>
</html>