Spooky Sarah created a challenge called 100 Horror Movies in 92 Days a couple of years ago. The difficulty factor is that they have to be movies you haven't seen before! This could be a problem for dedicated horror fans of a certain age, but there are resources for finding new-to-you movies.
Louise at Monstrumology explains how she has completed the challenge before, and how you can, too. You'll find link to many more resources at Metafilter. You might want to stock up on popcorn, too.
This will be a great experiment for those who are up to it. Or even those who aren't, because even if you don't get to 100 movies by Halloween, no one will know and you'll have a lot of fun watching horror films you never knew existed before. The 92 days starts on August first, so get to your TV now!