The Walking Dead #1, 2, 3, 4, 5, 6
Image Comics, 2003/2004.
This comic book series turned out to be very successful for Image with the TV series making its debut on Halloween 2010. However, when the comic book series was first published back in 2003 there were only small print runs for many of the early issues making them pretty rare. Once the TV series took off, the demand for the early issues exploded and prices rose steeply.
Things got even better during the second TV series with prices rising astronomically on the early issues with #1-6 now all worth over $100 apiece in NM and other key issues such as #19 (Michonne's 1st appearance) going for around $250NM and #27 (first Governor appearance) for around $175NM.
The story centers around the character Rick Grimes, a small-town police officer from Cynthiana, Kentucky, who was shot in a firefight and went into a coma. He wakes sometime later in an empty hospital and has his first meeting with the walking dead. The story then focuses on his search for his family and also to other survivors who have banded together with him.
Prices seem to have peaked each time the TV show aired with a lot of interest in Michonne who appears in cameo at the end of the second series (from issue #19) and, given the low numbers of these books and their popularity, they are likely to remain as top modern collectibles.
One last thing: it has been noted elsewhere that the initial print run of The Walking Dead #1 had the colors for the "MATURE READERS" warning printed in the wrong sequence so that the black lettering was printed on top of the white, which disappeared. This was noticed and corrected so the black on subsequent issues adds some shadow/depth to the white letters. However, it is worth noting that the CMYK printing process is subtractive and white is not generally printed (white is starting point i.e. the color of the paper) so it is almost certain that the black printing plate was changed or modified for the second batch.
Sources indicate that there are around 4,000 issues with the black lettering with the rest white, hence the white is rarer (although more white variants seem to come to market). The black lettered issues were printed first hence could be viewed as the first print with the white as the second print; the black lettered variant could also be viewed as an error variant of sorts. CGC don't differentiate between the two variants (they probably didn't spot the difference until many were graded i.e. too late) so this is probably just a storm in a teacup.