Although cabinets typically come in rectangular shapes, they don't have to, and neither do islands. Depending on the floor plan of the home, a triangular island may be preferable, offering a similar amount of storage and work space but a better walkway through the kitchen. A semicircle or half a hexagon create a "command central" vibe that keeps the focus on the island as a communication hub and the kitchen as the heart of the home.
By virtue of its shape, an irregular island stands out in any kitchen. Make it a focal point with architectural details such as open shelving and decorative molding, or use a splash of color for the countertop, stools or lighting fixtures.