What is the keyboard shortcut for "Open With" in Finder?

The best solution for me:

1. Select file you want to open
2. Press ⇧+⌘+/ (opens up the mighty Help search)
3. Then start to type a name of app you want to open
4. Use arrow keys to select right menu item
5. Press Enter
6. Done!

For example I want to open HTML-file with Sublime Text instead of Chrome. I navigate to this file, press shortcut, type in "su", press down-arrow and press enter!

I'm afraid there's not shortcut. You can, though, create your owns.

To do so just:

1. Go to System Preferences / Keyboard / Keyboard Shortcuts / Applications.
2. Click the + button.
3. Choose Finder, from the drop-down list.
4. On the menu title field add the exact name of the menu bar item. It this case it should be Other... instead of Open with.
5. Pick your keyboard shortcut and click Add.

You'll be able to test the shortcut right away. Just mind the Open always with option!

If you frequently open a file in a specific app (other than the default app), you can set a keyboard shortcut for doing it. This is super easy.

Let's say you want to open a file in Sublime Text whenever you press control+S after selecting the file.

1. Go to System Preferences > Keyboard > Shortcuts (tab) > App Shortcuts (option in left sidebar).
2. Create new shorctut by clicking/tapping on +.
3. Select Finder as Application.
4. Set Menu Title as Sublime Text (or Sublime Text.app, depending on your settings).
5. Set Keyboard Shortcut as control+S. It will be shown as ^S. Or you can use any other shortcut which you prefer.
6. Click/Tap on Add.

Now you can simply select the file and press control+S to open the file in Sublime Text.

As requested , here is a capture of [my blog] post for an Automator Service that works for me in Yosemite .

Code for Applescript in step 2

on run {input, parameters}

    tell current application to activate


end run

Code for Applescript in step 5

on run {input, parameters}
    set theApp to (POSIX path of (item 1 of input))
    repeat with i from 2 to number of items in input
        set this_item to item i of input
        tell application theApp to open this_item
    end repeat
    tell application theApp to activate
end run

After Saving the Automator Service go to System Prefs. and add your shortcut to it.