Don't mean to be too obvious or trite, but Holly and Ivy are nice ones for Christmastime. Of course, there's also Noel or Noelle. For Easter, if you recognize it as a religious event, you might want to try a name that ties in with the atonement, death or resurrection of Christ: Names like Grace, or Ransom (usually for a boy) might work. If you're willing to use names from other languages, there's Salvador or Salvatore, meaning "savior." I'm sure there's a host of others you could find among biblical names, such as Isaiah, Joel, Elijah, and so forth.