Relational Database Service (RDS)
It provides a SQL Server, MySQL, Oracle or PostgreSQL server, installed, configured and ready to use. AWS will manage the infrastructure: they will install the patches, execute the backups, resizing, availability (they will manage the failover, for example), etc. And our DBAs will manage the databases.
DynamoDB
It is a NoSQL database solution, we have to specify the performance we need, for example, 20 writes/second and AWS will resize the solution to provide it. It could store any amount of data, it has not limits. It is very easy to provisioning and resize the capacity needed for each table.
It is totally integrated with AWS Elastic MapReduce.
MapReduce is a Hadoop cluster, so it could manage petabytes of data. It converts a complex and vast process in an easy and effective process from a cost perspective.
Redshift
It is a data warehouse in AWS, it is optimized for OLAP. It can be escalated from 1 node 2TB XL to 100 nodes 16TB 8XL, and vice versa. You pay just for the infrastructure you provisioned, it is fully managed and compatible with SQL and all AWS services. It is optimized to work with AWS S3.
ElastiCache
It is a fully managed caching service. It is protocol-compliant with Memcached. It manages patching, detection and recovery of failures in a cache node. We need just a simple call to the API to grown or shrink the cluster. It is fully integrated with AWS CloudWatch (monitoring service) and AWS SNS (notification service) for monitoring and alerting, and supports Security Groups. Seamlessly caches in front of SimpleDB or RDS instances.
SimpleDB
It is a highly available and flexible non-relational data store that offloads the work of database administration. Developers simply store and query data items via web services requests and Amazon SimpleDB does the rest. It is optimized to provide high availability and flexibility, with little or no administrative burden. SimpleDB creates and manages multiple geographically distributed replicas of your data automatically to enable high availability and data durability. The service charges you only for the resources actually consumed in storing your data and serving your requests.
Angel Perez Palacios 