I was recently told that I am "hard to shop for." Au contraire! I'm a cinch to shop for. Anything food-related works, whether it's cookies or chocolate or kahlua-soaked brownies or gourmet cheese or jams. Good books are always appreciated, but I guess that depends on taste and trying to find something I haven't read yet. So here are some other ideas:
Scientific office toys, like those from think geek:
Nifty rock samples, like these meteorite chunks from here:
And last but not least, I can always use something practical. Say, the basic textbooks that didn't follow me out of college - something I'm not likely to buy for myself.
Or, you know, some local edibles...