As some of the PPs have said:
Boys are more common in day 5 fresh tx'ers. The reason behind this is that the male embryos develop at a faster rate and are therefore always seen as the stronger embryo (im sure most of you have been called with results with an embryo or 2 that is way ahead of the others in it's development - these are commonly the boys).
ICSI - due to the fact they have to catch the sperm the girls swim slower than the boys due to carrying more genetic code on them so they are easier to catch.
HOWEVER: in a frozen tx there is no way to know which embryo *was* growing the fastest at the time of freezing - they just pick one at random so anything goes.
I think if you've had boys so far after 2 cycles theres nothing saying you wont have a girl but the same DOES NOT apply the other way around imo due to the fact the fastest developing embies are always picked first which would be male if there were any male embies to begin with.
Some people do only have the 1 gender of children though even after have 5+ attempts LOL (non IVF and those who can afford to generally go down the IVF gender selection path in Thailand or the USA).