a good many
A large amount. There were a good many people doing last minute shopping at the mall on Christmas Eve.
a great many
A very large number of (people, things, etc.). A great many people have joined the protest to voice their concerns over increased taxes.
(a) good many
quite a few. I have a good many kinfolk in Texas. Mary owns a good many acres of land.
great many
see under good many.
a good/great many
very many; a lot: A good many people think she’s right.There are a great many places in the world I’d like to visit.