My wife and I want to visit the UK.
She has a Greek passport and I have an aufenthaltskarte (residency permit card for family members of nationals of EU).
Are we are free to travel or do we need other documents?
Yes, if you have a residence card for a family member of an EU citizen, then you do not need a visa to enter the UK when travelling with or joining the same EU citizen. If you travel without that EU citizen and are not joining them in the UK then you would need a visa.
Note that this might change when the UK formally exits the European Union.