Google checkout is an alternative - but to my knowledge does not support subscriptions yet. This is one of it's major shortcommings. It is also a bit less mature as a product.
But PayPal has been very slow to evolve since its initial success - so it will be good if Google gives them a run for their money. Ideally I'd like to see a 3rd competitor in the space.
After that you have to roll your own solution with a payment gateway and internet mercant account. Doable - but complicated.