On the MMBug Mailing List, there was mention of a couple of good dropdown menu sources that work on every browser. Here’s where it pays to buy software from someone who’s specialized in a very convoluted field: browser compatibility for tricky DHTML programming. I’m making this entry so I don’t forget, because this is a pretty common thing to need.
Ultimate Dropdown Menu from Brothercake. I like his site, and he’s a good example of a niche software guy that I would do well to emulate: know your stuff, be good at what you do, provide an accessible product, and present yourself well.
Milonic, which I looked into a while ago and ultimately didn’t use.
Coolmenus, which was what I used for one project once, but doesn’t seem to be actively updated any longer. The site is really slow too (I know, I’m one to talk).