Rss feed module.
You can choice between rss and xml.
You can select what product and category to be shown.
Demo http://demo.plusmotiv.com/opencart-1.5.5.1/index.php?route=common/rssfeed

i have separate module for 2.0 http://www.opencart.com/index.php?route=extension/extension/info&extension_id=21938 . If you have bought this module i will send you for free