Module Views Slideshow
Views Slideshow allows you to have rotating images or banners such as on a home page. This is very common technique on recent web sites. It also allows you to have pages or blocks that fade in/out, which is great if you to highlight particular items within your site.
Since it's based on views, the items can be nodes, teasers or selected fields from CCK (like an imagefield and text box/caption.)
There are many other similar modules that do rotation/cycling (http://drupal.org/node/418616) but this one is simple to use, obviously integrates with Views (important IMO), and contains its own API.