I've now bought a few of these Mental Notes decks for the Hashrocket offices. Each card (52 in all) has an insight drawn from psychology that can help you with brainstorming and problem solving. They arrive in an attractive faux leather box and the whole package seems like a great little Christmas gift. I'm not making any money from this referral -- I just think they're great.
Mental Notes (about $50 incl. shipping to US destinations)
Get the first 7 cards as a PDF download