Player handouts for sure. Remember TOMB OF HORRORS? Nothing quite like saying to your players, "You enter a vaulted chamber dripping with a strange, phosphorescent green liquescence. Your footsteps echo on the curiously dust-free stone floor as you approach a scrolled marble sarcophagus decorated with scorpion tails..." and then whip out the artist's rendering of that sarcophagus. Players eat that stuff up with a spoon.
So, why not offer a PDF of NPC "headshots" and memorable location artwork? A little more work for DUNGEON, for sure, but invaluable to the readership :)