Many families number a guitar player in their midst. This family member is the easiest on the Christmas shopping list - guitar care products, instructional dvds, a supply of guitar strings, a capo or even a new guitar would make perfect gifts.
A guitarist most likely already has a guitar but there is a range of products to help with the maintenance and playing of that instrument.
It can be difficult spending a little more on a guitar related Christmas present as the gift giver needs to know that the gift is going to suit and the non-guitar player may find that preferences can be difficult to predict. A good solution is to ask staff at the local music store that the loved one frequents, ask friends, band mates or their guitar teacher.
So - if the shopper is careful and thoughtful a guitar related gift is fairly easy to find. These are just some ideas, a visit to the local music store will reveal many others.