Experientia docet - Experience is the best teacher
Experimentum crucis - Critical experiment
Expressio unius est exclusio alterius - The mention of one thing may exclude others

Extempore

Without premeditation

Exterioris pagina puella - Cover Girl
Extinctus amabitur idem - The same [hated] man will be loved after he's dead. How quickly we forget. (Horace)
Extra ecclesiam nulla salus - Outside the Church [there is] No Salvation. (A phrase of much disputed significance in Roman Catholic theology)
Extra territorium jus dicenti impune non paretur - The judgment (or the authority) of one who is exceeding his territorial jurisdiction is disobeyed with impunity
Fabas indulcet fames - Hunger sweetens the beans, or hunger makes everything taste good!
Faber est suae quisque fortunae - Every man is the artisan of his own fortune. (Appius Claudius Caecus)