Ideal solution: unisex bathrooms. I don't really care who uses the toilet with me.
That's not going to happen though, because reasons (even if you think they are bad reasons). So IMO, transsexual people should just use the restroom for their birth sex - it's the only objective, simple, fair way of deciding who uses what restroom.
I know that's not what you want. I know some people might feel bad because they have to use the "wrong" restroom, but when you use the one you feel is correct, you make other people feel bad and their feelings are just as important as yours.
Please don't think I'm some kind of hateful bigot or something - I really don't care what restroom you use and I think all this legal nonsense about throwing people in jail for it is all a stupid waste of time.. However, if it has to be segregated - and for now it does (at least in america) since american culture won't accept unisex restrooms then we have to decide what criteria we use to determine who goes where. "Whatever restroom I want to use" is no good because it effectively makes all restrooms unisex, and that's something the majority of people don't want.
Re: "but but but the men kill us if we use the men's room", cite? I can only find ONE example of a transsexual being beaten up over using the restroom, and (surprise) it was two women beating her up for using the women's room. I found another example of a transsexual being killed in a (private, hotel) restroom but it was almost certainly unrelated to which restroom she used in public. if there's some sort of epidemic of toilet-induced rage killings (or solid evidence such a thing would occur) then I might reconsider my opinion based on a public safety standpoint, but I see no evidence that this is a genuine threat.
Re: special toilets for transsexuals. Transsexuals are less then 1% of the population (in most areas), even if we set aside all moral issues about it, it's just not practical to build a third set of toilets for such a small group of people, especially when there's no mechanical reason they can't use one of the existing toilets.