Floating Flower Tip - Most flowers float pretty well on their own until they start to pool with water and slowly sink. For a longer lasting centerpiece, use bubble wrap to make little skirts for your flowers.
Drink Umbrella Wreath - Here is a great fun idea for a summer wreath for your front door. Get a Styrofoam wreath and stick a ton of fun drink umbrellas in them. This would be so great to put out while hosting a luau or summer swim party.