Earlier this month i was trying to find a tree-view navigation menu to embend into a friend's web-site, one wouldn't expect that but people actually are willing to sell you one, anyhow i found this after a quick search
http://www.treeview.net/ - it's a free tree view menu, which is easy to install and use. Download package also provides demos, examples, guides and such (too many of them even, might scare off a user who just want a copy&paste thing, if you are that user you should just ignore them, untill you want to do a little customizing). In default state it looks like this
And, to not make a second post about navigation, if you would like a more standart drop-down menu, you should definately use jquery one, it's pretty straight forward, can see one, say, here
And it does exactly what it should do - a simple drop-down menu. Plus some extra features like more smooth timing of menu disappearing and such.
I hope that information was useful.