OMA in Rotterdam ("The Office for Metropolitan Architecture" or in Dutch, Grandmother) is currently working heavily with rich middle-eastern countries to design amazing cities and ports. In its long history, the firm has done amazing work.
MVRDV in Rotterdam recently won a competition for a new high rise in Copenhagen, shown on the right and top-left. The firm has been around since 1991 and appears to be quite progressive. A recurring motif in their work is delightful green spaces within and on urban structures.
BEAR Architecten in Gouda does smaller scale work with a specific focus on sustainability and using the local environment in several ways, such as water landscaping, passive solar, and solar photovoltaics. They recently won a competition to design a sustainable development of 255 CO2 neutral houses in Lelystad-South.