XML is the replacement for CVS (comma separated variables) files and just about every other structured data file, except for long lists, which are better suited to relational databases.
Data with an internal relationship, think chapters of a book, can be stored in one XML file with the chapter divisions defined via XML. When the book becomes too big for XML, you can place each chapter in a separate file and relate the chapters through a separate XML file or using a relational database. You can also store the XML in a database instead of a files. Continuous audio and video files, think radio and television, use other formats for compatibility with old analogue formats. Forget all the weird file formats, if you do not need a database, use XML.