C[0,1]. In fact if A is a commutative primitive C^*-algebra, then A has a nonzero faithful irreducible representation (H,j). So (j(A))¢ = C1. But j(A) is commutative, so j(A) Í (j(A))¢ = C1. But j(A) ¹ {0} so j(A) = C1. Thus A @ j(A) = C1.