You could use Superfish for this type of menu, although the CSS would be up to you to create. For the multi-column menu I would use multiple ul elements inside one parent li element and just assign them a width and float them next to each other. I know this works although I don't have any examples on hand.
You might get a better answer by posting this to a dedicated CSS list as I am unaware of any jQuery plugin that happens to provide the CSS for this, which is what you are really after. Once you have the CSS setup, then you can probably easily throw something like Superfish at it to give it the mouseout delay and IE6 support, etc. Joel Birch.
