If "run more regularly" is on your tentative list of New Year's resolutions, Runner's World's What Should I Wear? calculator can help you choose the appropriate running gear for your next outing.
On the face, it's a somewhat silly web app. You plug in the temperature, wind speed and sky conditions, then add how you prefer to feel when you run (cool, in-between, warm). Still, for a lot of people, running is an extremely difficult habit to pick up, and if you're starting your routine in the dead of summer, the last thing you want is to make your jog more difficult — so if you're never quite comfortable once you're in the middle of your jog, it might be worth a go.