Originally Posted by Nedim
Thanks for your input. I want to have a bike for road riding / exercise.
Sounds great. If you're doing purely road, then a road bike will do fine. Depending on brand, there are usually two types of geometries: racing (aggressive/low) and sport (comfort/upright). For example, Cannondale has their Synapse frame, which is less aggressive than their Supersix and EVO frames that are raced competitively on. Also (depending on manufacturer again), there will be aluminum and carbon fiber frame variants of each type - carbon fiber usually costing at least 2X more.
If pure road is not for you, there is usually a "hybrid" line, which is a cross between mountain and road frame geometries. Some like this if they find any of the road geometries uncomfortable for cycling. Usually you get road bike components with a much more upright stance. The handlebars are usually taken from mountain bikes and usually suits those who don't like the geometry of a (curved and more compact) road handlebar.
As a beginner cyclist, I'd suggest a more upright geometry so it's not too taxing on your back when you're just getting acquainted. That's the basics of the frame.
As far as components go, there is a range of brands (e.g. Shimano, Sram, Campagnolo) each has a range of models that go from entry level (Al/steel mix) to high end (full carbon fiber and lightweight alloys). These also dictate the overall cost of the bike. As a starter, I'd do something between entry level and mid-range so at least it's dependable in the long run.
Finally, wheels are the rotating mass on the bike and probably are the biggest mod you can make to a bike after you buy one. The heavier they get, the more effort you will end up putting in on longer rides (which isn't really a bad thing). The lighter they get, the more expensive they are! Usually, you get what comes with the bike and upgrade later on depending on your needs. In today's market, most wheels are dependable. For lower end bikes, I'd stick to the true and tried brands, which include Mavic, Fulcrum, Shimano, Campagnolo, FSA and DT Swiss.
Again, speak to someone at a local bike shop. Big stores are good to check out for the overall picture. Indy shops are also good because the guys usually give personal advice that the bigger stores may not.
Keep in mind that the bike is only part of the investment. Helmets, cycling clothes, shoes and other gear can also rack up quite a bill. If I find gear that I really like and want new, usually I size it at the shop and purchase it on eBay for a lot less. Good luck!!