One only has to step outside onto any parking lot to understand the meaning of "heat island" as pavement across the continent becomes too hot to touch. Asphalt is a fossil fuel product, it retains heat and is impermeable- a little rain and all the dirt, pesticides oil and dog crap wash into the storm sewers and waterways. Porous pavements let air and water pass through, filtering pollutants on the spot. Right now, their best feature is that they are cool. Azure Magazine's Material World section recently covered a series of options for paving that beat the heat and don't hold water. Open Cell Concrete Block is one solution- concrete paving systems designed to take the load of vehicles yet with enough open space that water can drain and grass can grow. The Hastings Checker Block shown above is 70% grass.
Hanover Architectural Products makes Eco-Grid (39% open)