org.el (org-time-stamp): C-u C-u C-c . inserts a timestamp with no prompt.

* org.el (org-time-stamp): With two universal arguments,
insert an active timestamp with the current time without
prompting the user.

This idea came up on the list, I can't recall who proposed this.
Thanks to him anyway!

lisp/org.el

@@ -15007,13 +15007,20 @@ Return the position where this entry starts, or nil if there is no such entry."
 
 (defun org-time-stamp (arg &optional inactive)
   "Prompt for a date/time and insert a time stamp.
-If the user specifies a time like HH:MM, or if this command is called
+If the user specifies a time like HH:MM or if this command is
-with a prefix argument, the time stamp will contain date and time.
+called with at least one prefix argument, the time stamp contains
-Otherwise, only the date will be included.  All parts of a date not
+the date and the time.  Otherwise, only the date is be included.
-specified by the user will be filled in from the current date/time.
+
-So if you press just return without typing anything, the time stamp
+All parts of a date not specified by the user is filled in from
-will represent the current date/time.  If there is already a timestamp
+the current date/time.  So if you just press return without
-at the cursor, it will be modified."
+typing anything, the time stamp will represent the current
+date/time.
+
+If there is already a timestamp at the cursor, it will be
+modified.
+
+With two universal prefix arguments, insert an active timestamp
+with the current time without prompting the user."
   (interactive "P")
   (let* ((ts nil)
 	 (default-time
@@ -15059,6 +15066,8 @@ at the cursor, it will be modified."
 		    (concat (substring org-last-inserted-timestamp 0 -1)
 			    " " repeater ">"))))
       (message "Timestamp updated"))
+     ((equal arg '(16))
+      (org-insert-time-stamp (current-time) t))
      (t
       (setq time (let ((this-command this-command))
 		   (org-read-date arg 'totime nil nil default-time default-input inactive)))