Because i have been asked for it, i made a list of free HDR photo tools for editing and creating those.
Here they are:
hugin for Linux, Windows and Mac
FDRTools Basic for Windows and Mac
Picturenaut for Windows
pfstools for Windows, Unix and Mac
Qtpfsgui for Windows, Linux and Mac
If you want to get further information about software for HDR editing and using the right converters for it take a look at the website of Panotools.
There is also a nice comparison between photomatix (commercial) and picturenaut (free) to be found here.