I've just started a new pre-paid service that allows you to launch an on-demand EC2 instance using bitcoins. Recharge amount starts at $5 and you will be billed at a flat rate
$0.12 per hour per running instance. You stop incurring charges as soon as you terminate your instance.
Check out the service here https://bitnodes.io/
The service is targeted for users needing ad hoc computing resource provisioned by Amazon Web Services without any commitment needed to monthly/yearly signup and certainly no credit card needed!
As this is an early beta release, first 100 users using the coupon code "bitcointalk" will get
$0.12 complimentary credit for free so you can launch and run an instance for an hour without any charges. It will be terminated automatically at the end of the hour though or when your balance reaches $0.00.
Let me know of your feedbacks here. Thanks!