I've updated to Flex 2 the code by Christophe Coenraets for embedding HTML in a Flex application using an iframe.
You can see a demo of it here.
You can download the code here.
To run locally, first compile IFrameDemo.mxml. If you are using Flex Builder, unclick "Generate HTML wrapper file" in the Flex Compiler settings before publishing, since there is an existing HTML wrapper. After this, you can view IFrameDemo.html. If you get a "Security sandbox violation" error, you need to put the IFrameDemo directory in the local-trusted sandbox. See the Flex documentation for information on updating FlashPlayerTrust files.
The one cause for limitations in this code is the use of opaque for wmode. I've seen reports of tabbing problems in the player, and running more than one player when using opaque wmode seems to degrade performance.
This update also includes minor improvements to the code for readability and polish.
Update: if you'd like to share your own experiences with HTML in Flex or read what others have to say, see my new post on this.
Update 2: see this post for an update to the code that allows multiple HTML pages to be referenced at once.
Update 3: see this post for an update to the code that needs less HTML changes, allows multiple HTML pages to be referenced at once, and controls the HTML visibility as needed.