When you think of the great science fiction book cover ilustrators, such as Freas, DeFate, and Powers, you have to include Darrell K. Sweet, who passed away on the 5th of December at the age of 77. I remember all the fantastic covers he did in the late 70s for Del Rey books. Between 1975 and 2005 he did over 3000 book covers. Amazing!
Here are just a few: