While there's a lot they COULD do with their war chest it ultimately boils down to this: They can take risks.
They're opening something like one store every two days for the next two (or is it three) months. They've just built a massive data centre for iOS and have the option to expand it (relatively) rapidly if required. They can afford to secure vast swathes of components even if they're not100% sure they will use the capacity they're buying and, in doing so, take that capacity away from rivals. They can introduce new products (like the iPad) and commit a LOT of resources to it because it doesn't matter if it flops, at least in money terms. They can move OS X delivery to the App Store and slash the price to a quarter of previous major OS X releases. They can make OS X server available for $50 instead of the hundreds of dollars their competitors think they can charge for a server licence. And on and on and on...
Of course they can also decide to grab a very big name should they choose but, at the moment, it's difficult to see anything that would really make sense. The simple fact is right now they don't need anyone else and any major purchase of another company would risk weakening both. Plus there's the uncomfortable problem of what will happen when Jobs leaves, having a ton of cash on hand for that transition might not be a bad idea.