I know this one seems like a no-brainer, but it still needs to be said. If excessive heat is a concern, you should rethink the outdoor ceremony and reception in the name of heatstroke.
My husband gave me carte blanche during the wedding planning process, but he had one very important request: Don't set the date during college football season. Since every month leading up to that sacred time of year was already spoken for except August, you can guess when we were married. Given that and the fact that we were married in Georgia, where humidity and mosquitoes the size of bowling balls run rampant in the summer, and you'll understand why everyone thought we were crazy.
Nevertheless, we plunged headfirst into planning the perfect indoor nuptials. In fact, the only time anyone was outside was when they walked from their cars to the various air-conditioned events. Incidentally, a random cool front happened to blow through north Georgia that weekend, making the high around 78 degrees. Beat that, springtime brides!