Output same content type in different format
The easiest would be to use Views Datasource which allows you to output any data in XML, JSON, XHTML with different schemas. You can the set your own URLs and can have fine control over the output.

Another, rather primitive way is to use the RSS feed with full content on, but I take it that may not be what you are looking for, yet when all else fails &mdash; it is better than nothing.