Could you really ask for any more? Now you can download vassal for 40k that includes the latest two codexes, Grey Knights and Dark Eldar. What is Vassal? For some it is a way to play 40k games online, for others it is a way to test armies out, while for most bloggers, it allows a means to visually demonstrate a tactical situation.
The new version is out today. My experience with it, shows quite the learning curve with the program, but check it out.
Here is the link. Vassal 40k 5.4E