A pork tenderloin is agreat choice that gives you a lot of leeway. You can search for a recipe to suit your tastes, apply a spice rub, or just purchase a loin pre-packaged and already flavored.
If you are looking to make a splash and have the grill to yourself, grill some dessert pizza's with fresh fruit, chocolate bits, and/or marshmallows. They make a great finisher to any barbecue.
Good judgement comes from experience. Experience comes from bad judgement.