Tell them Santa knows they've been bad. Give the gift of software. Make sure it's totally incompatible with the system it's to be run on. Don't give gift certificates. You know the recipient's tastes better than they do, and besides, you don't want them to know what a cheapskate you really are.
People love a challenge.
Better yet, hide the instructions and leave cryptic clues to the location. Make sure that you wrap your package in something with lots of glitter and tinsel. It'll never come out of the carpet, thereby ensuring that you'll be on their minds all year long. Wrap a large box with several smaller boxes inside. If you give clothing, make sure it fits and is flattering, so that you can borrow it often.