One neat feature of org-mode agenda is ability to display appointments in Emacs calendar. Sadly, this isn't obvious nor enabled by default - I discovered it accidentally by browsing through Emacs themes screenshots.

In screenshot below, you can see highlighted days with planned meetings and scheduled work in my calendar.

Setup is very easy. First, set calendar-mark-diary-entries-flag with:

(setq calendar-mark-diary-entries-flag t)

Then create $HOME/diary file, if not present, and add this line:

%%(org-diary)

Now in Emacs, open agenda view with (org-agenda) and open calendar with c; you will get highlighted all important dates. Alternatively, calling

M-x calendar

will essentially do the same (open calendar) with fewer strokes.

Reverse action will also work - to see what is scheduled for particular highlighted day, just point cursor to that day and hit key c - Emacs will open org-mode agenda view and place cursor under correct entry.

Using with appointments (appt)

In case you use org-mode with appointments to get visual reminders, be aware that calling (appt-activate 1) will run diary and making this call in your Emacs configuration will display diary window at Emacs startup, which I didn't like. To circumvent this behavior, appt-display-diary variable should be used.

In short, my appointments setup looks like this:

(add-hook 'org-finalize-agenda-hook
  (lambda ()
    (setq appt-message-warning-time 10        ;; warn 10 min in advance
          appt-display-diary nil              ;; do not display diary when (appt-activate) is called
          appt-display-mode-line t            ;; show in the modeline
          appt-display-format 'window         ;; display notification in window
          calendar-mark-diary-entries-flag t) ;; mark diary entries in calendar
    (org-agenda-to-appt)                      ;; copy all agenda schedule to appointments
    (appt-activate 1)))                       ;; active appt (appointment notification)