Brian Eno's Oblique Strategies
Oblique strategies is a set of over 100 cards designed by legendary producer and musician Brian Eno in 1974 to help artists (particularly musicians) break creative blocks by encouraging lateral thinking. Each card contains a phrase or cryptic remark designed to prompt creativity and brainstorming in new directions. They have been used by many famous artists since first created, probably most famously by Eno when working as the producer on Bowie's Berlin albums (Low, Heroes, Lodger).
This would be a fantastic and unexpected gift for any musician, writer or artist. You can read more about the background of Oblique Strategies here.