See here why. I would recommend this last order as the best if you are reading the stories for the first time, as it will enable you to discover the storylines in the order Asimov planned them. Also, some of the later novels are set before the earlier ones, but contain major spoilers for the earlier ones. List of all the books in the series in internal chronological order. List of all the stories in the series in internal chronological order.
Some people count 'The End of Eternity' and 'Nemesis' into the series.
I do not. In his introduction to 'Prelude to Foundation' he lists 14 books, and he has not mentioned 'the End of Eternity' among them. The same is true for 'Nemesis'. Although written after 'Prelude to Foundation', he could have mentioned in the Author's note that it was supposed to be part of the series. Of course, I might someday write another novel tying this one to the others, but then again, I might not.