Movie Bytes is a great site that catalogues screenwriting contests, giving you deadlines, entry fees and all the pertinent details. You can even sort, by genre, significance and read comments by people who have entered each contest. The comments can be a little snarky because, some of the commenters are pissed they didn't win. However, you can get an idea of which contests give you feedback and if the finalists or semi-finalists get calls from agents and managers.
**In my Biggie Smalls voice**So, scribes, if you don't know, now you know!