Dean Wesley Smith discusses cover design for indie publishers. Many good suggestions in the comments as well.
I’ve been experimenting with creating covers for my upcoming e-books (launching soon) and I really like Photo Pos Pro which is a freeware image manipulation program. So far, I have only experimented with photo covers, but some of my stories call for artwork to get the look I want. This is a bit of a problem, since I am a much better writer than artist. Still, we’ll see.
Gini Koch has a great guest post about finding one’s voice at Janice Hardy’s blog. The exercise she suggests sounds great, too. I will probably give it a try some day, even though my voice kicked in rather early during my writing attempts and it shines through, even when I deliberately try to write differently, e.g. my disastrous attempts to imitate the New Weird or Mythpunk voices which turned into parody within two paragraphs.