These are the Visual Studio extensions I'm more or less actively using. Descriptions are from the VSIX where I had nothing else to say. All are free (usually open source) on the VS gallery, except where marked as commercial.

VSExtensions.txt

SwitchStartupProject
Provides a toolbar dropdown box to switch between startup projects. -- VS 2015 has that too, but that doesn't recognize F# projects
https://visualstudiogallery.msdn.microsoft.com/f4e1be8c-b2dd-4dec-b273-dd88f8818571

Productivity Power Tools 2015
Color coded document tabs by file extension or project, various information in the scroll bar, column guides, etc.
https://visualstudiogallery.msdn.microsoft.com/34ebc6a2-2777-421d-8914-e29c1dfa7f5d

CodeLineage
Augments Visual Studio's built-in difference viewer with 'from' and 'to' revision sliders. Accessible from the 'Tools' menu, CodeLineage allows easy access to a cumulative diff view between file revisions. Supports SVN, Perforce, Git and Mercurial.
https://visualstudiogallery.msdn.microsoft.com/bb3d22aa-29bf-41e1-acc9-92482bee4646

StopOnFirstBuildError
Stops a solution build immediately after a project has failed to build.
https://visualstudiogallery.msdn.microsoft.com/91aaa139-5d3c-43a7-b39f-369196a84fa5

CodeMaid
Format document on save, C# class structure overview with Drag & Drop reordering etc.
https://visualstudiogallery.msdn.microsoft.com/76293c4d-8c16-4f4a-aee6-21f83a571496

MultiEditing
Set multiple carets with Alt+Click, make the same edits in all places.
https://visualstudiogallery.msdn.microsoft.com/2beb9705-b568-45d1-8550-751e181e3aef

Paket for Visual Studio
Manage your Paket dependencies from Visual Studio!
https://visualstudiogallery.msdn.microsoft.com/ce104917-e8b3-4365-9490-8432c6e75c36

Git Diff Margin
Git Diff Margin displays live changes of the currently edited file on Visual Studio 2010+ margin and scroll bar.
https://visualstudiogallery.msdn.microsoft.com/cf49cf30-2ca6-4ea0-b7cc-6a8e0dadc1a8

Smooth Caret
Smooth caret movement effect for the Visual Studio text editor. (As in newer Office versions; a bit sluggish on large solutions.)
https://visualstudiogallery.msdn.microsoft.com/b8721c44-5f1c-450d-a275-337791b0482a

Visual F# Power Tools
Better syntax highlighting, refactoring, linting etc. for F#
https://visualstudiogallery.msdn.microsoft.com/136b942e-9f2c-4c0b-8bac-86d774189cff

TabSanity
Navigate through tabs-as-spaces as if they were actually tabs.
https://visualstudiogallery.msdn.microsoft.com/ac4d4d6b-b017-4a42-8f72-55f0ffe850d7

Viasfora
Color matching braces, color highlighting of current C# block, enhanced keyword highlighting
https://visualstudiogallery.msdn.microsoft.com/19609469-380e-4fcf-bcde-e31caeb658b2

Target Framework Migrator
Change all your .Net projects Target Framework at once
https://visualstudiogallery.msdn.microsoft.com/47bded90-80d8-42af-bc35-4736fdd8cd13

ResXManager
Manage localization of all ResX-Based resources in one place. Shows all resources of a solution and let''s you edit the strings and their localizations in a well-arranged data grid.
https://visualstudiogallery.msdn.microsoft.com/3b64e04c-e8de-4b97-8358-06c73a97cc68

VSColorOutput
Color output for build and debug windows.
https://visualstudiogallery.msdn.microsoft.com/f4d9c2b5-d6d7-4543-a7a5-2d7ebabc2496

Export Extensions 2015.1
Provides an ability to Import/Export the list of Visual Studio extensions
https://visualstudiogallery.msdn.microsoft.com/a6a60f27-cf56-48c8-8ee0-b631716dd11c

ReSharper (commercial)
Refactoring, navigation, inspection etc.; no F# support
https://www.jetbrains.com/resharper/

NCrunch (commercial)
Very advanced continuous test runner
http://www.ncrunch.net/

OzCode (commercial)
Massively enhanced debugging UI/information; no F# support
http://oz-code.com/