Illustrator and Inkscape are the first two vector apps that come to mind. Inkscape is free, Illustrator is not. Most raster apps can handle the tiff files as well. Terragen does a really nice job of taking a tiff file and making it into a 3d terrain but it's not the easiest app to learn how to use properly. A newbie can turn out something halfway decent but "stunning" requires much more experience. Personally, I'd recommend looking at Inkscape first and see if it suits you.