Recently, I picked up the LWIS.NET CSS Dropdown Menu for a project that I’ve been working on.  In my opinion, this is a great menu system with a few different templates (horizontal & vertical) for easy customization.

The one trick that I picked up when using this template is that you need to add some code to get the drop down effect to work.  Basically, adding onmouseover="" inside the li elements with submenus will allow the hover CSS events to perform as intended.  By default, the iPhone will ignore hover CSS events unless you specify a onmouseover event handler (even if it is blank).  Thanks to commenter twenty205 for the original idea.