On package vacations, single travelers are often hit with a "single supplement" to the base price. To avoid it, you can agree to room with other single travelers or find a compatible roommate before you go, from one of the many roommate-locator agencies.
Canadian-based Connecting Single Travel Companions (tel. 604/886-9099; www.cstn.org) runs personal ads on its website from single travelers looking for companions; it also offers useful links to other sites.
TravelChums (tel. 212/787-2621; www.travelchums.com) is another Internet-only travel-companion matching service with elements of an online personals-type site, hosted by the respected New York-based Shaw Guides travel service.
Many tour companies offer singles-only trips. Singles Travel Company (tel. 888/286-8687; www.singlestravelcompany.com) offers budget-oriented singles-only escorted tours to places like Italy, Belize, and Egypt. All Singles Travel (tel. 800/717 3231; www.allsinglestravel.com) arranges Egypt tours with good hotels and possible extensions to see Israel as well. Backroads (tel. 800/462-2848; www.backroads.com) offers "Singles + Solos" active-travel trips to destinations worldwide.
For more information, check out Eleanor Berman's classic Traveling Solo: Advice and Ideas for More Than 250 Great Vacations, 5th Edition (Globe Pequot), updated in 2005.