Some of my favorite summer songs:
Beatles "Here Comes the Sun" and "Good Day Sunshine"
Cream "Sunshine of Your Love"
Jimi Hendrix "Long Hot Summer Night"
Monkees "Daydream Believer"
Bon Jovi "99 In the Shade"
Guns N Roses "Paradise City"
Van Halen "Dance the Night Away"
and just about anything by the Beach Boys.
Oh, I almost forgot one of the very best: Van Morrison "Brown Eyed Girl"
Hope this helps!