Since we can't seem to escape the news these days, I like today's quote.
Write the quote on the tag and add, "thanks for always seeing the cup as half full". If they are traditional, use china teacups. If they are more fond of modern or contemporary, find some clean lined white mugs. If they prefer a more artistic style, I found these porcelain ones on etsy. If you take it the extra step and match their style, you just made the gift relevant.