I've been using Pop-Up Menu Creator Pro by Anoxy Software
http://popup.jscentral.com/ for a few years now and have been extremely pleased with it. The menu size it generates is extremely small and the script is linked from the page which really helps cut down on load time.
This is a short description of the program from it's help file:
Pop-Up is a program for creating Dynamic Hypertext Markup Language (DHTML) menus for Web Pages.
With the Pop-Up menu creator you can create your own custom menus, easy and fast (without knowing any JavaScript), just with the push of a few buttons.
Pop-Up menu has many configuration options including; Horizontal or vertical menus, multiple color schemes, image insertion, description boxes, varied activation methods, autoscrolling and drag & drop facilities.
Support is excellent and any upgrades have been free over the years. Honestly, I cannot say enough about this program and the navigational menu it creates. It's definitely worth a few minutes to check out the site.
Suzn