One of the great things about summer is that wonderful warm night air. Watching the sky in the winter gets tough, but in the summer all we need is a dark sky and a patch of grass (to lie on). So summer is when I most enjoy one of my favorite things – watching people in orbit fly over me.
By far the most visible man-made thing in space is the International Space Station. NASA has made it very easy to see it by giving us a web page: you just put in your address and it tells you when the ISS will be coming by and even where it will be in the sky. The most visible times, of course, are shortly after sunset or shortly before sunrise when we are still in the dark but the ISS is bathed by sunlight.
Check it out. The NASA page is here: http://spaceflight.nasa.gov/realdata/sightings/cities/skywatch.cgi?country=United+States