If your world trekker enjoys venturing to countries where English is not the national language, opt for Rosetta Stone (or something like it because it is pretty expensive). Language learning systems are great gifts for anyone interested in learning a new language and hoping to use it on a future trip. Right now there are some decent holiday deals everyone should take advantage of.
They travel so much their luggage is starting to look a little worn out--and the fact that that zipper won't close all the way is a recipe for lost luggage disaster. Why not buy them a new suitcase? Or how about a whole luggage set? For those who practice tough love with their luggage, consider some serious baggage they will have a hard time breaking in. For something a little sleeker to suit that sophistacated type, there are some smaller, more creative, items you can look into.
Modern travel is not getting any more luxurious. In fact, making flying more enjoyable is next to impossible--unless you can afford those first class beds with private televisions and free champagne. So visit PB travel for cool accessories that make flying a little more tolerable. (Note: this website caters to women, but there are some pretty cool items.)
Something truly unique for a jetsetter is a personalized city map. Yes, you heard me right. A La Carte Maps combine the guidebook and the map in one easy to use tour guide which reduces the hassle of carting around a huge guidebook with so many places to visit it will make your head spin. You can get one made for a specific city, or there is the option to "create your own" city map where you can document the locations and adventures yourself. The possibilities are endless.
Finally, the best, and most obvious, gift for the traveler in your life: book a trip!