MODx's document data structure has been designed to allow many different routines to redisplay the information in ways that suit your needs, such as a dynamic menu in your template.
Since the last release of MODx, the community has produced many great snippets - reusable functions that you can call in your content or template. Two of the most widely useful are Ditto and Wayfinder.
Allows you to template every part of the menu. On this site, Wayfinder is being used to generate the drop-down menus, but many types of menus and sitemaps are possible.
Uses include listing the most recent blog posts, producing a site map, listing related documents (using a TV filter) and generating an RSS feed. You could even write a menu with it.
Archivist automatically creates navigatable archives from your posts. Filter by month, year, or even day!
If you can't quite get your desired effect using templating and the many options of Ditto and Wayfinder, you can write your own routine, or look for other snippets in the MODx repository. MODx's fields for Menu Title, summaries, menu position etc can be used via the API to produce anything you can imagine.