Anything that's an experience rather then an object - concert \ ballet \ comedy \ play ticket.
Anything that's handmade with love and attention to the person, crafts, paintings, art, mixed music CD, knitted scarf, a photo of themselves with you in a frame, a photo album.
A cool treat, like a massage, a spa day, a bottle of wine or fancy chocolate or other foods they can use in the holiday and wouldn't treat themselves to.
Make a donation on their behalf to a charity organization.