Mother Nature sees fit to hatch about 50:50, male to female. "Which is which," is surely the SECOND question people started asking about chickens.
I'm going to go out on a limb here and echo donrae:
The only reliable sexing method is sex link feathering.
This can be either with color or with wing feather length at the time of hatching.
And you're right, it only works with certain pairings.
Oh, sure, you will hear many lurid and colorful methods for determining sex, from hanging chicks upside down to swinging a sewing needle over their heads, pendulum fashion. My favorite is throwing an old hat in the air above them to see who "ducks" and hides - those are supposedly females
And like all of these "old fashioned" methods, this, too, is just lore and wives tale.
Of course, some one will now appear that says they knew someone, or tried what old Uncle Marvin told them great granny did, etc.,... and it worked. There is ALWAYS somebody to say that.
But we are offered only hearsay, they keep no records and they have nothing but anecdote to go on.
I can tell you this much: I have read many old poultry books from the 19th and 20th centuries and I can't think of one that offers any definitive method other than sex linking to determine boys from girls. Most of them recommended you just wait until it's obvious which are males - and then eat or sell off those you don't want.
If other sexing methods actually existed in that "mysterious" olden time we hear so much about, well, you'd think it would have been noted.