https://developers.arcgis.com/en/flex/guide/guide.htm
http://geochalkboard.wordpress.com/2010/02/18/introduction-to-the-arcgis-server-api-for-flex/
http://resources.arcgis.com/gallery/video/arcgis-api-for-flex/details?entryID=AC895780-1422-2418-34E4-EEAE95C2654A
but why flex when you have javascript.