It is based on the existing plugin 'Article Table of Contents' but because it didn't had all I wanted to have I reworked the settings and fixed the code to work with my Joomla installation and produce valid XHTML 1.1.

To use it you have just do install and enable it and adjust the settings to your needs. If you want to disable it for certain articles just place {autotoc enabled=no} inside the text.
You can also go the other way round an disable generating a ToC by default and place {autotoc enabled=yes} (or simply {autotoc}) inside the text of articles where a ToC should be displayed.

If you want to choose a different layout for the ToC in different articles you can select either the table layout or the dropdown layout in the global settings as default, and select another visualization with placing eg. {autotoc layout=table} inside the according article.

Updates:

0.17.7:
- Fix possible PHP warning.

0.17.6:
- Hide {autotoc} tag in smart search preview.

0.17.5:
- Fix for error with some automatic code minifiers.

0.17.4:
- Fix PHP strict warning.

0.17.3:
- Spanish translations (Thanks to marcanuy!)
- Bug fix with Joomla 3.2 (Thanks to Rajoz!)

0.17:
- Allow setting 'float' (=alginment) per article.

0.16:
- New per article parameters 'addNumbering' and 'addNumberingToc' to select whether the headings should be numbered on a per article base.

0.15:
- Add option to select default state of ToC if using 'hide' link.

Older notable updates:
- New option to show a wikipedia like 'Hide' link for ToCs using table layout.
- Add new option to add additional views where the ToC should be displayed.
- The plugin should now work with both FLEXIcontent and K2.
- Thanks to Frank Thommen there is now a Joomla 1.6 compatible version.
- Established compatibility with the pagebreak plugin:
* Add toc after page navigation
* Changed css class of toc from 'contenttoc' to 'autotoc'

Download for Joomla 1.5: http://www.tomprogs.at/downloads/joomla/joomla-plugin-inhaltsverzeichnisse-fuer-artikel/download.xhtml