I just read a thread on KS that mentioned a sexing method that I've never heard of before. This method involves the same technique as popping, only to the point of opening the vent and not actually popping the snake. Supposedly the male has more blood vessels in that area due to the hemipenes and will appear more pink whereas a female will appear a very light pink or even beige. The guy included pictures, and the difference seemed pretty obvious.

Seems like it might come in handy for those females that don't exactly probe the way they're supposed to.