Almanacs, atlases, and thesauruses are wonderful, inexpensive reference works that are a must-have for serious writers. You can even decrease look-up time and avoid the tiny print in the paperback versions of world almanacs if you can find ones you like on disk or online.
World almanacs list about anything you could ever want for basic research. You can even use them to name your characters. For example, when naming a foreign character, look up his country of origin, scan the current government leaders for a last name, combine that with the first name from the country’s history (say, a war hero), and bingo, you have a legitimate, ethnically accurate name.
Almanacs also give the gross national product, offer tourism information, and list major industries and resources. They show which countries are on the metric system, so when your character is racing through a metrics-using country in a rental car, he’ll buy fuel in liters.
If your characters travel the world and you want them to be believable, use a world atlas. You have to know time zones, current country names, monetary units, populations, average temperatures, etc. Atlases provide detailed maps, and internet atlases even offer street maps — crucial to realistic action scenes.
When you use a thesaurus, don’t make it obvious that you have done so. Inexperienced writers tend to find the most exotic word in the thesaurus, when a thesaurus should ideally be used to remind you of alternative ordinary words that best convey your meaning.
Using a world almanac, world atlas, and thesaurus makes it easier to get minuscule details right, which makes for a more entertaining read. When you get the details wrong, they’re suddenly not so minuscule anymore.