Latin was/ is probably the hardest course I have taken at university but it's kinda cool to know it.  Some of my favourites:
Nemo me impune lacessit: Nobody/no one provokes me with impunity (motto of Kings of Scotland, and now Scotland herself)
fortes fortuna adjuva : Fortune favours the brave
ad victoriam: to victory (war cry of Roman soldiers)
Carpe Cerevisi - Seize the beer!