It's going to be the long hard slog of brand building and domain authority. Earning links using great content is crucial to long term success. Fortunately, Hipmunk seems to be doing a great job of getting those strong trusted links. Just take a look at their press page! Their UI and core product is the great content that's earning them press mentions here which is awesome. Making a core product that is good enough to earn links is the win-win of online marketing. Get the full story at the SEOmoz blog