My favorite melon varieties are Athena (cantaloupe) and Passport (honeydew) They ripen in August to early September depending on how warm and sunny the summer is. They haven't had any powdery mildew, but I don't really have the right conditions for P.M. to take hold. My method of growing healthy melon plants is to give them a little mulch to prevent the soil from splashing onto the leaves, make sure they get a lot of air circulation, and make sure they get all day full sun. They need good rich soil that drains well and consistent water but not to the point of being wet. I always get a good crop of melons this way unless the weather is unusually cloudy, wet, or cool.

Last year I had great luck with "Minnesota Midget" cantaloupe. They are small (about 4-6" in diameter) and very sweet. I got 5-6 melons per plant (I had two plants). They held up incredibly well to our dry summer last year. I had mulched slightly but otherwise didn't worry about them, save for watering along with the rest of the garden. I had no problem with powdery mildew. (Though I may have had to try very hard for pm to develop last year!)

Good Luck!