XML
XML is crap. Really. There are no excuses. XML is nasty to parse for humans, and it's a disaster to parse even for computers. There's just no reason for that horrible crap to exist. - Linus Torvalds
Boost.PropertyTree55
A property tree parser/generator that can be used to parse XML/JSON/INI/Info files. [Boost] website
X
Xerces-C++
A validating XML parser written in a portable subset of C++. [Apache2]