For Apple to maintain the lead they have had they need to continue to innovate new types of products, not just keep improving what they have. I think there is plenty of opportunity for this. Think smart appliances, houses, cars. The question is whether they still have the ability to do that with Jobs gone. Time will tell.

Edit: Probably the most likely new category would be wearable computing now that I think about it. Longterm perhaps electronics integrated with the body.