For the time being there's only one word I feel an urgent need to argue for - TRANSSEXUALISM !
A frustrating anomaly is the frequent use of the unintelligible word Transsexuality - meaning what? Crossing our sexuality? As we pass the 'natural' division between the sexes, not between different sexualities, the -ity form really makes no sense.
This linguistic misunderstanding probably stems from the closeness between the gay and trans communities - in reality as well as in most people's minds - which makes the grouping of "homo-, bi- and transsexuality" come quite naturally - in spite of the lack of basic similarities with respect to sexual core identity.
An example is when Pat Califia, in her book "Sex Changes", refers to numerous books and articles on the subject of Transsexualism, but chooses Transsexuality for her own text ...
... and an even more recent one is history professor Joanne Meyerowitz, who does exactly the same in her 2002 book "How sex changed". In her Introduction she even manages to end one sentence with a footnote containing three references to "transsexualism", only to start the next with "Transsexuality". A few pages on she claims that the -ism form was used mainly in the 50s and 60s - a contradiction in itself, as the word was made accessible to the public only with Harry Benjamin's 1966 book - and is now generally replaced by the -ity variety. Is it really? In her footnotes she refers to a number of papers on "transsexualism" also from the mid 90s, but there are few to back up her claim of a general change.
There's also Deirdre McCloskey, who for her lovely book "Crossing" chooses the "sexuality" alternative, and then goes to lengths to explain that it really has nothing to do with this - sexuality, that is. Why not, then, go for "transsexualism", which leaves this problem behind from the start? You don't have to explain, and you won't be misread or misunderstood. These are major advantages, the way I see it!
The fact that even transsexuals frequently use the sexual denomination - and this in spite of the -ism form having been the scientifically accepted one since Harry Benjamin's groundbreaking work in the 60s - shows how deeply rooted the association with sexuality regrettably is.
We transgress the borderline between the biological sexes, not our sexuality - hence Transsexualism.