There is always the Rapid Environment Editor which claims full support for all major OS versions, including 64-bit.
Editable tree
Show environment variables and values as an editable tree.
Portable mode
RapidEE doesn't require installation and could be run as a "portable application". View details.
There is also the older (but still useful) and more light-weight Path Editor. (Note that the site is dead as of 2015-08-07, but still exists as an archive.org snapshot from 2013-03-27 — direct link to the installer). It works just fine on Windows 7 and, though it comes only as an installer, also works as a portable/stand-alone executable if you extract itextract it.
Path Editor is a small utility that makes path management very straightforward with its intuitive user interface and drag-and-drop simplicity. Path Editor can clean your path of missing and duplicate entries with a single click of the mouse.