Mapping

• Spacehulk Tilesystem
  Want to create your own spacehulk maps using great looking artwork? This tool makes it easy. Quickly create a space hulk map using tiles from the impossible to get a hold of official Spacehulk games and export to JPG or PDF. Awesome.

• 'Token' Images by Ik'kaan [BROKEN LINK - I'm asking permission to rehost, hope to have them back soon]
  Good set of tokens and other images for mapping and virtual tabletops. You can download them all at once using links on the left.

 Atmospheric Sound Mixing & Effects

• Scene Sound  
  I tried a lot of different programs to let you mix music, atmospheric sounds, and sound effects with gaming in mind.  This is the best of the bunch in terms of ease of use and functionality.  It also happens to be free, although donations are appreciated!  
   
• RPG Sound Mixer 
  If you need something more advanced that Scene Sound you can try your luck with RPG Sound Mixer.  This application does not appear to be under current development and may have difficulties working on modern OS'. It does however have some pretty advanced scripted mixing features. It is not free but has a demo.