Help for Groom's Outfit

Let me start by saying this is a second wedding for both of us, and we are not doing the white gown/tux/catering hall thing again. We're getting married Aug. 29 in the evening at a Vineyard, about 80 people. I am wearing a light pink cocktail dress with some sequins. FI wants to dress somewhat casually -- he says this time he gets to chose what to wear. Except he doesn't know what to wear!! He is against a suit because it will be 'too hot' and he wants to be less formal. Any ideas??? Anyone????? His poor BM is banging his head because he doesn't know what to wear either!

Thanks.