I've recently listed several designs that feature mason jars, which are pretty much the quintessential summer decoration. They are proving to be very popular with summer and early autumn brides too!
I just designed this matching save-the-date card today:
This design has fireflies too. It reminds me of a summer evening wedding:
I've got some more great summer designs in the works...think ice cream, polka dotted sea animals, and sweet little lovebirds!