By default, browsers place embedded plug-in content, such as a Flash movie or Java applet, on the topmost layer. In older browsers, attempts to place a DHTML layer on top of a Flash layer would fail.

The solution is to use the WMODE parameter to allow layering of Flash content with DHTML layers. The WMODE parameter can be 'window' (default), 'opaque', or 'transparent'. Using a WMODE value of 'opaque' or 'transparent' will prevent a Flash movie from playing in the topmost layer and allow you to adjust the layering of the movie within other layers of the HTML document.

• Flash content displays on top of all DHTML layers
• Joshuaink: Flash content and z-index

WP-Cumulus allows you to display your site's tags, categories or both using a Flash movie that rotates them in 3D. It works just like a regular tags cloud, but is more visually exciting. Clicking the tags can be a little hard (depending on your speed setting) but does take you to the appropriate page :).

• WordPress plugin: WP-Cumulus Flash based tags cloud | Roy Tanck's weblog
• Cumulus - drupal.org