AWS EC 2 ~ Free Usage Tier (Per Month)

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 Amazon EC2 Microsoft Windows Server‡ 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*

30 GB of Amazon Elastic Block Storage, plus 2 million I/Os and 1 GB of snapshot storage*

source
http://aws.amazon.com/free/