Musicians, at least in my personal experience, can be an extremely hard group to please when it comes to gift giving. They want to look cool, not corny, so ties with guitar strings or piano keys are definitely out.
I'm unsure about the sound quality of the folding guitar below, but its space-saving design sure would be beneficial on weekend trips for gigs. And for the wannabe guitarist who happens to play the keyboard, or vice versa, there is the guitar-piano hybrid which consists of 24 strings on 24 frets.
Drummers always have a lot of equipment to take with them. A USB drum kit would be a great alternative way for them to practice without having to lug their drum set back and forth.
Although the easy-to-please musician would be happy with having the newest and greatest musical instrument or gift, it's a good idea to let the pickier ones (like my hubby in the photo) view them and decide for themselves before buying. For a safe gift, however, most guitarists would appreciate a nice guitar strap or tuner. Lastly, for any musician who writes lyrics and/or music, the piano-style journal is an excellent choice to write their creative ideas down on paper.