Most people are familiar with the suckerfish style drop down menus, but as a quick recap they are lightweight CSS driven dropdown menus.

I won't go into massive depth here, but suffice it to say that there have been many improvements to the way they work, and the most streamlined version I've come across is here:

http://www.htmldog.com/articles/suckerfish/dropdowns/

It's a good article on how to get them working on your site, and how they interact with different browser versions.

What is quite interesting though is that there is an issue with them in IE7. If you use the 'sticky' version of them (where the menu stays visible even after mouse out) then IE7 has a CSS flaw in the handling of it.

As the link under here explains, there is a fix for earlier IE versions that creates a pseudo class to get them to work as they should, but IE7 handily circumvents this to break.

http://css-class.com/articles/explorer/sticky/

This entry details how to fix the IE7 bug and end out with a totally cross browser CSS friendly version.