Which sites offer the best/accurate deals? Travelocity, Expedia, other?

Of those sites that are out there, do any offer deals on train fare or is it strictly flight/hotel accomodations? The gnome was featured repeatedly on the Amazing Race, and I guess the implication with Expedia is that they can go anywhere with Captain Kirk. Seriously though, which have you used, were they any good/bad/ok and why?