HDRsoft (the creators of Photomatix) offers a free trial version of their latest software. It has no expiration date, allowing you to test its capabilities, though it does add a watermark to saved images.
If you're looking for a cost-effective way to access Photomatix Pro, consider the following alternatives: Photomatix Pro 4.2.6 License Key Torrent
A completely free, open-source GUI application that provides a wide range of HDR tone-mapping engines. HDRsoft (the creators of Photomatix) offers a free