1. Η δραχμή and το χιλιάρικο, and other names of coins etc.

However, many Greeks, when naming prices, don't count drachmas, but count coins or banknotes. So here are some common names for money: πενηντάρικο = a 50 dr coin, κατοστάρικο = a 100 dr coin or banknote, πεντακοσάρικο = a 500 dr banknote, χιλιάρικο = a 1000 dr banknote, πεντοχίλιαρο = a 5000 dr banknote. Κατοστάρικο and χιλιάρικο especially are used for naming amounts of money. So, instead of τριακόσιες δραχμές, you may hear τρία κατοστάρικα, and instead of τέσσερις χιλιάδες, τέσσαρα χιλιάρικα. Note that the names of coins and banknotes are neuter, not feminine, so they take the neuter forms of numerals!

Male	Female
-ος	-ου
-ας	-α
-ης	-η in general, but usually:
-ίδης	-ίδου
-άδης	-άδου

Note also that a male name ending in -ος and accented on the third syllable from the end becomes a female name in -ου accented on the second syllable from the end; so, Παπαδόπουλος becomes Παπαδοπούλου. This has historical reasons and does not tie in with how the genitive would be formed today; "Mr. Papadopoulos's car" would usually be "Το αυτοκίνητο του κ. Παπαδόπουλου", with accent on the third syllable from the end. Names ending in -ας or -ης hardly ever have the accent on the third syllable from the end, and when they do, the accent stays the same, e.g. Μπούκουρης becomes Μπούκουρη.

Something that may be confusing is that the the female name endings -α and -η look like female endings, and you may be tempted to decline them. However, they are masculine endings in the genitive case and do not change.

So, if you have a car belonging to Maria Peraki, then it is "the car belonging to Maria, (wife) of Perakis" — το αυτοκίνητο της Μαρίας Περάκη; not της Μαρίας Περάκης! Her first name, Maria, has a feminine ending and forms the genitive regularly by adding -ς; her family name, though, is a genitive and cannot form another genitive, so it stays the way it is. Similarly, it's το αυτοκίνητο της Ελένης Παπαδοπούλου.

Male names that do not end in one of the usual endings stay the same in all cases, and the female equivalent is then identical. This is particularly the case where the male name ends in -όγλου or is a genitive form such as Σταύρου, Παπαθανασίου, Χατζηιωάννου.