Though the problem with a textbox is it's incompatible with the "display the aggregate results publically but keep people's privacy" option.

That's true, and why I said if possible. I think the textbox option works better if the survey taker is going to report on and discuss the results, making their own charts (which I've seen people do for fun/curiosity), or if a person is writing their own survey script.

Personally, if its a checkbox/button style survey, I'd rather click 'other' than try to puzzle out what the survey writer and other survey takers are assuming when they list trans/genderqueer/intersex (together or separately, and if under questions about sex, gender or both). Of course, I'm sure others will disagree; as long as the survey taker is defining the choices on sensitive subjects like this its not possible to please everyone.