This will start out to be an incomplete list, but should grow with time.
Last update Feb 10th 2016.
These are links that are sometimes handy to have when the UI doesn’t display them.
|Path and file||explanation|
|_layouts/viewlists.aspx||Same as site actions->View all content|
|_catalogs/masterpage/Forms/AllItems.aspx||View master pages for this site collection.|
|_layouts/changesitemasterpage.aspx||Changes the master page for the site collection (must be called from the site collection url, not a subweb url)|
|_layouts/permsetup.aspx||assings the 3 magic groups to a sharepoint web called from a web or subweb url|
|_layouts/chkperm.aspx||Check user permissions and group membership in given Web *|
|_catalogs/lt/Forms/AllItems.aspx||List template Gallery|
|_catalogs/solutions/Forms/AllItems.aspx||Site Template (/Solutions) Gallery|
|_catalogs/users/simple.aspx||This looks at the secret internal users list on a site collection – I had to do this once when dealing with an Active Directory migration and having duplicate users show up when they should not.|
|_layouts/user.aspx||A list of all groups and users in a given Site|
|_layouts/groups.aspx||A list of all groups in a given Site Collection|
|_layouts/AreaTemplateSettings.aspx||This screen chooses what site templates are available when creating a new site in a given site collection|
|_layouts/quiklnch.aspx||An almost odd list view of the quick launch items –
but not the one you get to from site settings.
This is linked to from the “getting started” web part.
|_layouts/qlreord.aspx||Same as above – this one lets you sort the quick launch items.|
|_layouts/AdminRecycleBin.aspx||End User Recycle Bin.|
|_layouts/AdminRecycleBin.aspx?View=2||Deleted from End User Recycle Bin.|
|Pagename.aspx?contents=1||View the web parts on a page – good for times when a web part keeps a page from rendering in normal mode.|
|_Layouts/appinv.aspx||view details about an app (2013/2016/SPO)|
* Thanks to reader Jacek Bulwan for submitting this one!