What i found:
People will say different thing below me, but this is what works for me every time.
Meths - Bit in the bottom of a coke can, cut top off, put pads in (enough to just cover the pads), set it alight. When all the meths has burn away, remove (be careful, hotness).
Put meths on a lint free, new, clean rag and rub all over disk braking surfaces.
Team Nick Wood
Hot water and washing up liquid using a pan scourer
buy some muc off or some alcohol free detergent
Turps Should Do The Job
have heard hover it over the hob on the oven, til it starts to get hot or you can tell the oil is burning off, then drop it in some water. That is ment to work, have not tried it yet though
hot water and fairy, but dont forget that the pads will have soaked up the oil
I burn the oil off my pads/rotor using meths, has worked for us lot well over the past couple of years.