There are two main considerations in choosing a road bike: frame material and componentry. The frame material is a big contributing factor to ride quality as well as to cost. Similarly, you will often find significant price differences on otherwise equal road bikes based on the choice of components.
Frame Materials
Bikes are generally made of one (or sometimes a combination) of these materials:
* steel - least expensive; heaviest material to work with, though weights have come down in recent years; flexible, shock-absorbant; "steel is real"; smaller tube diameters, Reynolds tubing, 631 and 853 series tube sets are most current; will corrode, especially in salty environments; long-lasting
* aluminum - inexpensive; very lightweight; very stiff; translates road shock more than other materials; recent tubing called 6000 series (very good) and 7000 series (even better); can be shaped into aerodynamic designs; tubes are larger to help dissipate road shock; cannot corrode, but does fatigue over time
* carbon fiber - more expensive; unique tube shaping achieved by layering carbon sheets; generally a tad heavier than aluminum, but lighter than steel; some manufacturers approach light aluminum weights, but at great cost; very plush ride; can be stiff, depending on bike design; long-lasting, though carbon fibers do "loosen" after many thousand miles
* titanium - most expensive; some manufacturers use commercial grade TI to bring costs down; feels like steel, plush like carbon, can be as stiff as aluminum; 3/2.5 means 94.5% ti, 3% alum., and 2.5% vanadium; 6/4 is the most expensive tubing; should last indefinitely, as TI does not corrode
In general, bikes costing $1,000 and less will be made of aluminum. You can find a bike with a carbon fiber frame in the sub-$1,500 range if you look hard enough, but there are likely some tradeoffs involved. Titanium made frames - as well as other exotic materials like Scandium and even bamboo - sell as complete bikes for over $2,500 in almost all cases. There is a "sweet spot" right between $1,200 and $1,800 where, if you look around enough, you can usually find a great bike - solid frame, very good components - for a great price.
Litespeed Firenze - titanium road bike
Components
The next thing to know about selecting a road bike is components. There are three main component manufacturers: Shimano, Campagnolo, and SRAM.
* Shimano- made in Japan
o Dura-Ace- best quality, big price tag
o Ultegra- just a notch below D/A, excellent
o 105- still top shelf, 1/2 pound heavier than Ultegra
o Tiagra- big drop-off in quality, start of affordable level
o Sora 2- heavier, still fairly reliable- 8 or 9 speed
o Sora 1- entry level- 7 speeds (hard to find)
* Campagnolo- made in Italy
o Record- best quality - carbon shifters - expensive
o Chorus- very high quality
o Centaur- medium level components (formerly Daytona)
o Veloce- heavier, much less expensive, black or silver
o Mirage- entry level - has compact option
o Xenon- entry level - 10 speeds
* SRAM - made in USA
o Force- best quality, unique shifting
o Rival- high quality, lower price point
Choosing the components (or "grouppo") is important because you want shifters that feel right in your hands, that respond when you click them; you want brake levers that you can grip from multiple hand positions and that feel solid when they are bringing you to a fast stop; you want derailleurs that move the chain into gear smoothly without clunky shifting. Also, components wear over time - higher end components will last longer.
Shimano Dura Ace Group
Why are there such big price differences between component groups? The higher-priced components are machined as finely as possible to save weight; they use titanium screws and bolts in some cases; they are machined more precisely than lesser components. That is to say, what makes components better quality is better materials going into them, more time spent to machine them to exacting standards, and weight savings.
Road bike forks are made of carbon fiber, aluminum, or steel. But realistically, aluminum and steel forks have an effective resale value of $0. Any road bike you look at today should have a carbon fiber fork.
Finally, there are all the other bike parts to consider: saddle, seatpost, stem, handlebars, wheels, tires, and pedals. Most bike manufacturers buy bike kits in bulk in order to save on their bike builds. So it's typical to get a "family" of bike parts from Ritchey, Profile, or another top parts maker on a new road bike. The quality of parts certainly matters, but for the purpose of this buying guide, we won't get into too much detail here. Suffice to say that you will want a saddle that feels good, so you may want to do a little research on the saddle listed to see what others have said about it. Frequently, one swaps out the stem on a new road bike in order to get the right bike fit, so keep this in mind. Most new road bikes do not include pedals, but if yours does, that's a bonus.
Armed with the information above, and disregarding name brand (although it is certainly important), here is a rough guideline for pricing road bikes (assuming very good to excellent quality):
* aluminum, steel- tiagra, sora- $400-$600
* aluminum, steel- 105- $700-$1,100
* aluminum, steel- Ultegra- $900-$1,800
* aluminum, steel- Dura Ace- $1,500-$4,000
* carbon, TI- 105- $800-$1,500
* carbon, TI- Ultegra- $1,200-$3,000
* carbon, TI- Dura Ace- $1,800-$5,000
* aluminum, steel- Veloce, Mirage- $400-$800
* aluminum, steel- Centaur, Chorus- $800-$1,800
* aluminum, steel- Record- $1,500-$3,500
* carbon, TI- Centaur, Chorus- $1,000-$2,500
* carbon, TI- Record- $2,000-$5,000
