Mosso CloudFiles
Now as the author of Net::Amazon::S3 I was overjoyed. I'm in the middle of rewriting that module to make it more flexible and take full advantage of the S3 service. But there's no point having backup in the cloud if there is only one place to back up, so I bought some chocolate and some Coke, hacked for an hour and released Net::Mosso::CloudFiles last night.
The Cloud Files API is clearly based on the same ideas as the S3 API, but it's slightly simpler: it is a clean REST design with plain text responses (instead of XML) and good use of HTTP response codes. The main difference I've found so far is that one of the great features of Amazon S3 is that listing a bucket (container) also gives you the ETags of the files. It looks like in CloudFiles you have to do a HEAD request on each file to get the same functionality at the moment. Otherwise, looks nice.