Ink for their printer, special paper, or even the paper that makes cards or good Business card paper. If you want to go to the trouble of making presents, make some stationery for your friends. You could make them paper with letterheads. Office Max and Office Depot sell lots of different papers. If you have grandchildren, or young children of your own, you can make them stickers.
Children love stickers.
A box of CD blanks would be nice. We are always getting CDs and not all come in hard plastic cases. A file box would be nice to keep those computer receipts and instruction books. Computer games are a nice addition to put in someone s Christmas or Hanukkah stocking. Last but not least you can make your own t-shirts using your printer and an iron on decal.