I, too, had always thought that travel agents added little value. As a result I would investigate Expedia and Travelocity, and then book directly on the airline's web site (to get the bonus miles). However, I recently had an experience which changed my outlook:

I am flying HKG to SFO for Christmas and wanted to make the trip on United to make 1K this year. The web sites (including United Connection) indicated the least expensive fare available on United was $1900 (coach). This seemed rather high, so I called a travel agent. She got me on the same United flights for $900.