After installing Sloeber (the Arduino plugin for Eclipse), the software installation sites were deleted. This will prevent Eclipse from making updates to the installed plugins. These are the sites that I use with my Eclipse for PHP Developers setup which can be restored manually through Help -> Install New Software -> Available Software Sites.
- Neon
http://download.eclipse.org/releases/neon - The Eclipse Project Updates:
http://download.eclipse.org/eclipse/updates/4.6 - org.eclipse.e4.ui update site
http://download.eclipse.org/releases/neon/201610111000 - EGit P2 Repository
http://download.eclipse.org/egit/updates-nightly/ - LiClipseText p2 Repository
http://www.liclipse.com/text/updates - Pydev p2 Repository
http://www.pydev.org/updates/