Well, there are a lot of options out there to choose from. You could go raster program like Photoshop, Painter, Paint Shop, or Gimp (free). Then there are vector programs like Illustrator, Inkscape and CorelDraw. Then there are things like Campaign Cartographer, Fractal Terrains, and Autorealm. I'd suggest that you look through the Finished Maps section to see what grabs your eye and then look at the author and under his/her name we try to list what software we use. You could also look through the Software Discussion thread for more ideas on programs.