Hairline theory - If your first born has a point to the back of their
hairline then you will have the opposite gender next time and if its
straight then you will have the same. With my youngest son he has a
point at the back and low and behold Im having a girl (hopefully lol)
This link might explain better http://www.whattoexpect.com/blogs/mylittlemonkeys/baby-gender-prediction-ive-found-the-secret
Mumma/Dadda theory - If you first born says mamma first then you
will have a girl next and dadda a boy. All my boys apart from my
youngest said dadda first, my youngest was the first to say mamma first
:)
Lots of funny owt on this site http://www.hisboyscanswim.com/658/list-of-51-pregnancy-old-wives-tales-your-babys-sex-revealed
A very interesting one was the skin under left eye one as I do actually have a v blood vessel!
I
dont put much faith in the owt because like I say most pointed towards
boy but it is fun to pass the time and when it does point to the desired
gender it can give a little hope 
Im not sure about the Ramzi
theory with myself, I know my placenta is anterior but its sort of in
the middle so I dont have a clue if it started left or right. I know on
my scan pics my girl was lying on the left which means flipped she would
actually be on the right, another reason why I convinced myself it was
another boy! I also had a bfp very early on and have had sore boobs more
so with this one than my boys.
Even the heartbeat is that of a
boy! Only thing I did hold a lot of faith in was the nub guess on which I
had nearly all girl guesses and it seems it can be quite accurate.
Hope the links help pass some time

x