A lot of times, people want very specific functionality out of a jquery menu. There are at least 5 or 6 decent jQuery accordion menu plugins out there. But they're all overkill in my opinion.
A jQuery accordion can be as little as 3 lines of code. Here's one in 7 lines of code. And if you do some chaining, probably even less.
$('#accordion li ul').hide();
$('#accordion li a').click(function(){
$(this).parent().addClass('selected');
$(this).parent().children('ul').show('fast');