Subcategories in Menus

Not sure if this is the best place for this (i.e. can it be done just in a template in a neat way or if it should be a feature request?) but would it be possible to create "groups" by subcategory in a menu (e.g. debenhams.com or next.co.uk to see what I mean although it's quite common on many stores)

There's plenty of modules / extensions out there that enable multiple-levels of drop down, but that isn't really what I'm looking for.

I suppose another option would be hard coding the menu as part of the header in my custom template (and then could maybe expand it to include images as next.co.uk does, but I expect there's a simpler way.