Originally Posted by hamster

There are four "big" brands, which, taken together, probably account for something like 80% of the "serious road bike market" (as in, everything above the Sport Chalet / Big 5 level, sold in dedicated bike shops). These are: Specialized, Trek, Cannondale, and Giant. They compete directly with each other, their model lines are pretty well matched in features and prices. Specialized and Trek are the biggest two, and both of them are full-spectrum manufacturers (making everything except for drivetrain - from frames to saddles to wheels). Cannondale is a bit smaller but still significant, and primarily focuses on bikes. Giant is the biggest of all in terms of worldwide sales, but it's not as well known in the U.S. because it's not an American company (unlike the first three, which are formally American but make most of their bikes in Taiwan, Giant is Taiwanese through and through.)

Colnago is Kim Kardashian of road bikes. It is famous because it's famous - but no one is quite sure why any more. It's been around forever (it was a major manufacturer of high-end racing bikes in the 60s and 70s, before Specialized, Trek, and Cannondale even existed) and it built up huge brand recognition which it uses to sell unremarkable bikes for 2x the price of matching Cannondales. The same describes a few other brands like Pinarello and Orbea.

Then there are some "specialty" brands (e.g. Cervelo, which specializes on light aerodynamic carbon frames, and Surly), and a bunch of smaller brands that try to compete with Trek/Specialized/etc but lack the market share (e.g. GT or Raleigh).

If you're interested in a carbon bike and you live in Iowa, you should pay extra attention to aerodynamics. Cannondale is good but it does not make any aero-specific frames. Take a look at Specialized Venge and Giant Propel.