You probably know this egg already, if you've played the game, but I decided to add it for completeness.

In Nashkel village, outside the Temple of Helm, there are numerous gravestones. Clicking on them tells you the epitaph written on them (most of which are quite funny).

Reading one of the stones on the east side triggers an easter egg - a sorceror called Daer' Ragh appears (anyone know who he represents?) And tells you not to do that again.

If you read the tombstone again, he reappears with a squad of phoenix guards who will slaughter your party, so make sure you've saved before trying this!