Depending on whether your "expert" to know more about the structure of "nanotechnology" or whether it will be more interesting Aboriginal distant islands, try to guess yourself. But if you could not guess – choose dictionaries and encyclopedias of general subject. Importantly, do not take anything too much for children and very popular – experts, usually theoretically savvy people, and all sorts of charlatans see through. If an expert – a real bookworm and an incurable bibliophile, and you are very low on money, you can give him the e-book. With this newfangled device it will save a lot of places in the apartment, as well as a lot of money in his own purse.
After all, the book in electronic format fb2 are mere pennies compared to paper counterparts, and the place and does not occupy. A special screen of this device – the so-called "Electronic ink" – a specially adapted for reading, so that your eyes will suffer much less damage than, for example, when reading from a computer monitor. If the selection of books put you in a dead end – select subscribe to the magazine. "Around the World", "Popular Mechanics" and other similar publications will be pleased and experts, and their growing up smart children. Search for unconventional solutions, and loved by connoisseurs guessing even more than ready-made facts and solutions. So look for a beautiful gift puzzles and quizzes. Classical Pentamino, Tangramom and Rubik's Cube "experts" are unlikely to be surprised (though who knows, maybe he wants to indulge in nostalgia and just that Cube itself is not enough for happiness).