You might be interested in Picturenaut. It can do all kinds of cool HDRI goodness, including create 'fake' HDRIs from conventional images and IIRC, you can use it to convert between the HDR mapping formats. There are also a lot of great free HDRs for download at the parent hdrlabs site in the Smart IBL section (http://www.hdrlabs.com/sibl/index.html) - you don't need the plugin to use them.

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