The post content is filtered by kses, but you can extend the list of allowed tags. A search in the plugin directory for kses shows some useful results.
Try Extend KSES, it seems to be exactly what you need (I haven’t tested it):
This plugin extends the HTML functionalify of the WordPress kses.php file, which states the allowable HTML that the post/page content editor will accept.
It allows the site administrator to check pre-defined HTML tags that can also be allowed via the editor. Tags include:object,embed,param,iframe,mapand extensions have been added to thedivandimgtags.