Tachyon.Net is a free astronomy software for Pocket PC. From their website:
TachyonNET for Pocket PC .NET is an extremely sophisticated and detailed astronomy software for handheld devices. It was developed to be a companion in your night cosmic adventures. It is by far the most complex and advancing astronomical software for those fantastic and small gadgets. You will not find anything like that. This is not a toy, it is an advanced astronomical companion that is indispensable for your next Star Party. Forget that bulky power hungry notebook. Put the sky in your pocket.
Check out the
VGA screenshots - they look unbelievably great!