Key shortcut (hotkey) in Visual Studio to open a file inside your solution?

The accepted solution doesn't work on the newer versions.
For Visual Studio 2022, and 2019, 2017 do the following:

Update 1:
Now, pressing Ctrl + Shift + T and typing the file name works!

Update 2:
Since Visual Studio 2019 now it's possible to do a similar search via Ctrl + Q.
But it works slightly sloppy since it shows VS-related stuff as well.

Original answer:

1. Press these keys to open the "Go to" popup:
   Ctrl + ,
2. Type there:
   f Space Filename
3. Press Enter

Notes:

• We are writing f to make VS search only on files. We can also, use other letters. For more info type ? in the "Go to" popup.
• For more keys and for Visual Studio 2012 to 2015 take a look at this answer.

This answer is outdated; see here for latest information.

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Not a single keystroke, but yes: `Ctrl+D > o f filename` (so that's five keystrokes before you start typing the filename). It then autocompletes the filename for you.

You need the Find box in the toolbar for this to work.

(If you change your mind about addins, SonicFileFinder is for this very purpose, and free.)