Amazon's Simple Storage Service. In essence it lets you read and write files
to web storage programmatically. The files themselves are located on
Amazon's servers. The service is excellent value, with modest charges for
data traffic and storage.
A neat feature is that all files are urls, so you can email links or
integrate into your web site. There's a permission system so that you can
make files private, world-readable, or readable by specific individuals.
Another advantage is no limit on storage space.