I was able to do a quick analysis of US government data about a year ago when the 77% thing was at it's height, and the industries with the largest raw discrepancy were Business and legal services. Tech was ~94% if I recall. I'll see if I can dig it up again.
You're talking about whether men and women in the same field get roughly paid the same. That's a separate issue from the ratio of men to women in the field.
edit: Here's an updated version for 2015: http://www.bls.gov/cps/cpsaat39.htm
edit2: And here's a curated google doc where I calculated the gender gap for each occupation with sufficient data: https://docs.google.com/spreadsheets/d/15vJGu8IMbvrVz6FqCg3r...