Subreddit Gender Ratios
http://bburky.com/subredditgenderratios/
This is really cool tool. It shows gender ratios of many subreddits. I personally find it useful because it allows quantification of gender interest in different topics. Currently there is a big social/media movement to pick various areas, highlight a gender difference in that area, and then attribute it to barriers being placed to stop one gender entering that area. This data can be used to help show that there are intrinsic variations in interests between men and women, and those should be considered in addition to the role of those entry barriers.
For instance: Psychology: 65.0% male / 35.0% female Economics: 89.6% male / 10.4% female Austrian Economics: 97.8% male / 2.2% female Physics: 89.2% male / 10.8% female Relationships: 48.4% male / 51.6% female