Joomla is so flexible and top notch product which supports all type of web technologies into it.  Yes i really mean it.  Joomla template developers use technologies from javascript drop downs to mootools . 

 Nowadays virtually any type of menu is possible for Joomla.  Well, honestly, while we look into drop downs, we have to take care of search engine optimized menus also.

 ok , if you need quicker solution, then go for "suckerfish dropdown menu".

And here we tell you why you should go for suckfish and how does it help on optimizing for search engines. 

When you use old type of javascript based menus, the front end behaviour of menus are generated wholly by javascript.  Technically , they use "document.write" for printing menus.  As search engine bots do not read such statements, they can not see your items too.  It means suppose if your site contains a menu item name "Pet cleaning service" by javascript menu, search engine will never see that link and will not crawl too.  So, what  you see in search engine index is nothing but homepage only.

Suppose if you use suckerfish menu, search engines will love to crawl your pages.  It is because simply sf (suckerfish) uses 90% css and 10% of js only.  Moreover, the front end menu generation is completely done through UL and LI tags with href tags.  They are clearly visible to search engine bots. 

We support any menu system that generate front end menu items in UL and LI.   Most of the time SF menu comes useful for this type of operations.

To download templates with SF menu, you can Google it ( :D  ) else, you need to join template club like themesclub or joomlart .  They both provide nice collection of menu items and good templates too.

(My English is not so good, thanks for reading)