Res severa est verum gaudium - True joy is a serious thing. (Seneca)
Res tantum valet quantum vendi potest - A thing is worth only what someone else will pay for it
Respice finem - Look to the end

Respice post te, mortalem te esse memento

Look around you, remember that you are mortal. (Tertullianus)

Respice, adspice, prospice - Examine the past, examine the present, examine the future (look to the past, the present, the future)
Respondeat superior - Let the superior answer (a supervisor must take responsibility for the quality of a subordinate's work)
Resurgam - I shall rise again
Revelare pecunia! - Show me the money!
Revera linguam latinam vix cognovi - I dont really know all that much Latin
Rex non potest peccare - The king cannot sin