I've needed to build static x64 library libiconv on windows - found two useful links. Leave it here. On June 2015 this article & project builds last version of iconv library.
Article with describing of building - link.
Project for visual studio, made by this article - link. It already has settings for lot of building variants - and static x64 too.
libiconv is widespreaded unix gnu library for conversion between encodings. iconv - console utility, which uses this library. Mostly I encountered with it in gunwin32 utils - no one util will work without this dll. But also it appears as dependency in some gnu projects - for example, libxml (added: it's appeared that libxml builds successfully without libiconv - don't know why - either icov optional, or iconv embedded into libxml).