We have just released a first beta of our DOpus Universal Graphics Viewer Plugin (utilising the excellent GFL graphics library), with support for HDR (and lots of other formats - see plugin About dialog for full list of supported file extensions). We hope to add support for EXR in the near future.
You can grab it from zwickysoft.com/download.htm
There are a few things to finish off, including the website, but you can use it to view HDR files.
Please contact us with any comments, suggestions and bug reports.