Amazon Elastic Cloud (EC2) for free

Amazon has a program to help users get started in the cloud for free. It is called AWS Free Usage Tier and it is offered as no charge for new Amazon EC2 customers.
You can run a micro instance for free for a year with a fairly good pack of services for free:

• 750 hours of Amazon EC2 Linux Micro Instance usage (613 MB of memory and 32-bit and 64-bit platform support) – enough hours to run continuously each month
• 750 hours of an Elastic Load Balancer plus 15 GB data processing
• 10 GB of Amazon Elastic Block Storage, plus 1 million I/Os and 1 GB of snapshot storage
• 5 GB of Amazon S3 standard storage, 20,000 Get Requests, and 2,000 Put Requests
• 15 GB of bandwidth out aggregated across all AWS services
• 25 Amazon SimpleDB Machine Hours and 1 GB of Storage
• 100,000 Requests of Amazon Simple Queue Service
• 100,000 Requests, 100,000 HTTP notifications and 1,000 email notifications for Amazon Simple Notification Service
• 10 Amazon Cloudwatch metrics, 10 alarms, and 1,000,000 API requests

Go on and check their offer as it might have changed.