JPG and RAW viewers

I have been using a new program (to me) for viewing my photos called FastPictureViewer ( http://www.fastpictureviewer.com/ ). I find it works really well and is especially suited to photographers. You can view your RAW images as well as quite a few other formats but it doesn't read .dng files without purchasing a codec pack. Does anyone else use this program? If so what are your thoughts or if not what are you using?

Thanks,
Peter