Back in October I pointed you to Amazon's Simple Storage Service (S3) (see Amazon S3, Now with SLA!) as well as their Elastic Compute Cloud offering (see Cloud Computing with Amazon).

Now, they've got another exciting new beta service on offer, Amazon SimpleDB, which is (per Amazon):

...a web service for running queries on structured data in real time. This service works in close conjunction with Amazon Simple Storage Service (Amazon S3) and Amazon Elastic Compute Cloud (Amazon EC2), collectively providing the ability to store, process and query data sets in the cloud. These services are designed to make web-scale computing easier and more cost-effective for developers.

Traditionally, this type of functionality has been accomplished with a clustered relational database that requires a sizable upfront investment, brings more complexity than is typically needed, and often requires a DBA to maintain and administer. In contrast, Amazon SimpleDB is easy to use and provides the core functionality of a database - real-time lookup and simple querying of structured data - without the operational complexity. Amazon SimpleDB requires no schema, automatically indexes your data and provides a simple API for storage and access. This eliminates the administrative burden of data modeling, index maintenance, and performance tuning. Developers gain access to this functionality within Amazon's proven computing environment, are able to scale instantly, and pay only for what they use.

For another viewpoint on what SimpleDB is good for, check out what Charles Ying has to say about it in What You Need To Know About Amazon SimpleDB. I'll just quote his bullets on what makes SimpleDB so cool:

• Really large data sets
• Really Fast
• Highly Available - It’s Amazon. Running Erlang. Whoa.
• On demand scaling - Like S3, EC2, with a sensible data metering pricing model
• Schemaless - major cool factor for me here; items are little hash tables containing sets of key, value pairs

What I love about Amazon's range of web/database offerings is that they reduce the entry fee for building massively scalable applications to almost nothing--you can get started for pocket change, and you only start paying through the nose when you start using lots of resources. Even then, the prices are still pretty reasonable.

If you're interested, you can check out the Amazon Developer Connection website, where they have articles like Scalable Media Hosting with Amazon S3 to help you understand what they're offering and how to use it.

What do you like (or hate) most about Amazon Web Services?