rst-link.el

(require 'google)
(require 'ido)
(require 'rst)

(defun rst-link (prompt-for-text link)
  (interactive "P\nsLink: ")
  (let ((text (if prompt-for-text (read-string "Text: ") link)))
    (if prompt-for-text
        (insert (format "`%s <%s>`_" text link))
      (insert (format (if (string-match " " link) "`%s`_" "%s_") link)))
    (save-excursion
      (unless (re-search-forward (format "\.\. _%s:" link) nil t 1)
        (goto-char (point-max))
        (unless (eq (current-column) 0) (insert "\n") (forward-line 1))
        (insert (format ".. _%s: " link))
        (insert (ido-completing-read "URL:\s" (google-result-urls (google-search-web link))))))))

(define-key rst-mode-map (kbd "C-c C-l") 'rst-link)