Exeter International 800/633-1008; www.exeterinternational.com. Tours of Eastern Europe, Russia, and Asia, including private tours of the Hermitage and palaces of the czars as well as gala dinners in some of St. Petersburg's historic houses.
Fischer Travel In return for a $10,000 membership fee and a $5,000 annual retainer, Bill Fischer provides 24-hour personalized service for travelers who care more about quality than cost. His number is famously unlisted.
Heritage Tours 212/206-8400; www.heritagetoursonline.com. Arranges excursions throughout Morocco, Turkey, Spain, and South Africa; treks in the Atlas Mountains and through the desert are Heritage's forte.
INTRAV 800/456-8100; www.intravalacarte.com. Since 1959, Intrav has led luxury group tours focusing as much on the mode of travel—plane, boat, or train—as on the destination (for instance, the $62,000 per person, 24-day around-the-world Concorde jet trip). Earlier this year the company launched Intrav A la Carte to arrange customized European and Asian travel.
Ker & Downey 800/423-4236; www.kerdowney.com. Best known for traditional African safaris—particularly in Botswana—during which travelers typically sleep in tented camps rather than lodges.
Maupintour 800/255-4266; www.maupintour.com. The company's MaupinFlex department arranges alternatives or add-ons to their vigorous adventure tours, which take place mostly in North and Central America. Also runs a Travel for Women program.
Mountain Travel Sobek 888/687-6235; www.mtsobek.com. This esteemed outfit established itself 32 years ago with a trek to Nepal, and today it's known for expertly planned outdoor adventures, from explorations of the Galápagos Islands to hikes through Italy's Lake District.
Off the Beaten Path 800/445-2995; www.offthebeatenpath.com. Designs explorations of wilderness areas in North America—the Rockies, Alaska, the Southwest—as well as Patagonia.