The Eclipse way
Installing Eclipse usually does not require to separately download any binary, since Eclipse provides a special mechanism to install and update plug-ins.
The GNU ARM Eclipse plug-ins update site URL is still on SourceForge:
More details are available in the Install page.
For previews, experimental releases are posted to a separate update site:
Sometimes you can use this site to test some features that are not completely implemented, or that might change before a final version is released.
This site is not always updated; use it carefully, back up your workspace, and do not use it for production projects.
The local archive way
If, for any reasons, you need to revert to a specific version, or the Eclipse mechanism to install new software fails, you can always download the desired version and manually install the plug-ins from the local archive.
Navigate to the Latest release page (or the desired version) and download the attached archive, it should be a zip file with a long name like:
Please note that not all plug-in versions run on all Eclipse versions, and usually new plug-in versions may require new Eclipse versions, so better try to stay as up-to-date with the Eclipse as possible. (For Eclipse Luna 4.4 and later, use versions 3.x; for Eclipse Kepler 4.3, use versions 2.x; for older Eclipses, try the final 0.5.5 version, but keep in mind it is no longer maintained).