There's an excellent article about the value of travel agents, written by Post-Gazette travel editor David Bear.  He mentions that travel agents book 87% of cruises, 81% of all tours and packages, 51% of airline tickets, 47% of all hotels and 45% of all car rentals.  He also points out some of the many services that travel agents provide.  Of course, not all travel agents are created equal, so it's important that you find an agent that you enjoy working with and that works well with you.