T.S.
My girls were always happy with new art supplies: fresh paper, markers, beads, colored pencils, play dough, crayons, etc.
Focus on things that will actually get used vs. just getting more toys. Books, DVDs, CDs and games for example. Or things they can play with outside, like skates, tricycles or sleds (if you have snow!)
Kitchen activities are fun too, my daughter got a snow cone machine for her birthday a few years ago and she has used it over and over.
Another option instead of stuff is activities: tickets for a show or play place, a month's worth of tumbling or skating classes or a gift certificate to a fun place like Chuck E Cheese.