U.S. online consumer travel sales (airline, hotel, rental car, cruise and vacation package reservations) will reach nearly $94 billion, up 19 percent from just under $79 billion in 2006, according to eMarketer.

Online travel sales are projected to remain strong for the next three years, albeit with steadily declining growth rates: eMarketer projects U.S. sales to reach nearly $146 billion in 2010, up from nearly $127 billion in 2009 and $110 billion in 2008.

A tighter market will exacerbate the fierce competition between online travel agencies and travel suppliers, according Jeffrey Grau, eMarketer senior analyst and author of the report "US Online Travel: The Threat of Commoditization."

This year, U.S. online travel bookings will for the first time surpass offline bookings in volume, according to PhoCusWright. In 2007, some 41.3 million U.S. households - some 52.5% of all US online households - will book travel online, according to eMarketer.

It projects that in 2010 nearly 10 million more U.S. households - 51.1 million, or 55.3 percent of all online households - will do so.