Amazon S3:

Amazon S3 provides a simple web services interface that can be used to store and retrieve any amount of data, at any time, from anywhere on the web. It gives any developer access to the same highly scalable, reliable, fast, inexpensive data storage infrastructure that Amazon uses to run its own global network of web sites.

Quite interesting. Iff you want to keep your data offsite. Amazon says they use S3 themselves and hope to deliver 99.99% availability. There is quite a bit of documentation on using S3 with different programming and scripting languages (Java, Perl, PHP) and it is a pay by use model: you pay per GB of storage in a bucket and you pay per GB of data transferred. No setup costs.