August is fine if you are prepared. This is the time most people come to Greece because this is when most people have their holidays and what could be better than to be close to the sea during the hottest months of the year? It's more crowded and rooms on the islands are harder to find, but the island nightlife is jumping and the beaches are lively. Athens can be pretty hot in the day but mornings and late afternoons are fine and the nights in the Plaka and Psiri are wonderful if not a little crowded. There will always be plenty of
Things to do.
Athens empties in August especially the week of the 15th and this is a great time to be in the city if it is not too warm. You can get good deals at many Athens hotels in August. If you plan to be in Athens during these months make sure you stay in a hotel with air-conditioning.
You can use the link below to look at Accomodation if you havent booked already.
http://www.destination360.com/europe.../athens-hotels