Keyboard shortcut to select Application "quit unexpectedly" dialog
Those windows are shown by the UserNotificationCenter process, so you can focus them by opening UserNotificationCenter with Alfred or Launchbar.

It is also possible to disable the crash report dialogs completely:

defaults write com.apple.CrashReporter DialogType none


This script can also be used to focus other windows shown by background processes:

tell application "System Events"
    repeat with p in {"UserNotificationCenter", "SecurityAgent", "CoreServicesUIAgent"}
        if exists process p then
            tell process p
                if windows is not {} then
                    set frontmost to true
                    exit repeat
                end if
            end tell
        end if
    end repeat
end tell


SecurityAgent shows password dialogs and CoreServicesUIAgent shows Gatekeeper and quarantine dialogs.