I read somewhere recently that the only "reliable" indicator is whether or not your boobs have grown in pregnancy. If they do, it's more likely to be a girl (something to do with raised oestrogen levels?) I have to say, in my first pregnancy my boobs didn't grow at all and I had a boy. In this one my boobs have grown much more and I'm having a girl, but tbh it's probably just because they've done it all before and have stretched a bit! All the others are definitely old wives' tales...a gender scan is the only way to know for sure!
Google the nub theory and gender. Quite interesting read. Basically every baby at 12 weeks has a little nub where the privates are. It's the angle of the dangle which tells you boy or girl. Pointing up is a boy and parallel girl. I predicted my first correctly using this method and two other friends! Make sure to get scanner to get a photo showing the nub during 12 week scan