The following icons are from GNOME 2.6:

    attach.xpm (stock_attach)
    connect.xpm (stock_connect)
    contact.xpm (stock_contact)
    delete.xpm (stock_delete)
    describe.xpm (stock_properties)
    disconnect.xpm (stock_disconnect)
    exit.xpm (stock_exit)
    lock-broken.xpm (stock_lock_broken)
    lock-ok.xpm (stock_lock_ok)
    lock.xpm (stock_lock)
    next-page.xpm (stock_next-page)
    refresh.xpm (stock_refresh)
    sort-ascending.xpm (stock_sort-ascending)
    sort-column-ascending.xpm (stock_sort-column-ascending)
    sort-criteria.xpm (stock_sort-criteria)
    sort-descending.xpm (stock_sort-descending)
    sort-row-ascending.xpm (stock_sort-row-ascending)

    gnus/toggle-subscription.xpm (stock_task-recurring)

    mail/compose.xpm (stock_mail-compose)
    mail/copy.xpm (stock_mail-copy)
    mail/forward.xpm (stock_mail-forward)
    mail/inbox.xpm (stock_inbox)
    mail/move.xpm (stock_mail-move)
    mail/not-spam.xpm (stock_not-spam)
    mail/outbox.xpm (stock_outbox)
    mail/reply-all.xpm (stock_mail-reply-to-all)
    mail/reply.xpm (stock_mail-reply)
    mail/save-draft.xpm (stock_mail-handling)
    mail/send.xpm (stock_mail-send)
    mail/spam.xpm (stock_spam)


The following icons were contributed by Adam Sjgren <asjo@koldfront.dk>:

    mail/preview.xpm (combining stock_mail and stock_zoom)
    mail/save.xpm    (combining stock_mail, stock_save and stock_convert) 


The folling icon are duplicated from Emacs 22.  They are either not present in
Emacs 21 or look different there.

    cancel.xpm
    close.xpm
    copy.xpm
    cut.xpm
    diropen.xpm
    help.xpm
    home.xpm
    index.xpm
    jump-to.xpm
    left-arrow.xpm
    new.xpm
    next-node.xpm
    open.xpm
    paste.xpm
    preferences.xpm
    prev-node.xpm
    print.xpm
    redo.xpm
    right-arrow.xpm
    save.xpm
    saveas.xpm
    search.xpm
    separator.xpm
    spell.xpm

You might want to use the following code to get Gnome icons in Emacs 21:

  ;; Only for Emacs 21:
  (when (and (not (featurep 'xemacs))
  	   (not (boundp 'image-load-path))
  	   tool-bar-mode)
    (push "/path/to/etc/images/" image-load-path)
    (setq tool-bar-map (make-sparse-keymap))
    (clear-image-cache)
    (tool-bar-setup))

The GNOME's stock_*.png files were converted to XPM using the following GIMP
script:

;; -*- scheme -*-
;; Put this file in ~/.gimp-*/scripts/
;; gimp -i -b '(rs-save-as-xpm "foo.png" "foo.xpm" 127)'  '(gimp-quit 0)'
(define (rs-save-as-xpm filename filename2 threshold)
  (let* ((image (car (gimp-file-load RUN-NONINTERACTIVE filename filename)))
	 (drawable (car (gimp-image-get-active-layer image))))
    (file-xpm-save RUN-NONINTERACTIVE image drawable
		   filename2 filename2 threshold)
    (gimp-image-delete image)))
;; end
