scala> Stream.iterate((0,1)){case (a,b) => (b,a+b)}.take(10).toList
res0: List[(Int, Int)] = List((0,1), (1,1), (1,2), (2,3), (3,5), (5,8), (8,13), (13,21), (21,34), (34,55))

scala> Stream.iterate((0,1)){case (a,b) => (b,a+b)}.map(_._1).take(10).toList
res1: List[Int] = List(0, 1, 1, 2, 3, 5, 8, 13, 21, 34)


こんなのも
def fibFrom(a: Int, b: Int): Stream[Int] = a #:: fibFrom(b, a + b)

参考URL
http://eed3si9n.github.com/scala-collections-doc-ja/