Domains with a “.com” extension are by far the most valuable and recognizable names. This is because Internet users will tend to remember and gravitate toward “.com” domains by default. This will tend to cause, for example, domains with a “.net” extension to lose significant traffic to their “.com” counterpart.  "Generic/Global Top Level Domains" (called gTLDs, which include, .com, .org, .net, .edu, .info, .biz, .mobi, .name, etc...)  other than .com also require your customers to remember and additional piece of information.  The primary goal of your domain name strategy should be to make your domain as mnemonic as absolutely possible so that your customers will be able to easily find your site again, and so that potential customers who have only received word-of-mouth information will be able to locate your business on the web with minimal or no effort.

So while you should always use a .com TLD whenever possible, be aware that there are many very excellent domain names which use either other gTLDs (i.e., .net, .org, etc...), or two letter country code domains called National or ccTLDs (for example, .us, .ca (Canada), .cn (China), .jp (Japan), and .co.uk (United Kingdom)), which represent some important exceptions to this rule.  The best aspect of using this broader range of TLDs is that you can still find very memorable, effective names for a fraction of the cost of a .com domain.  The following are some important aspects related to using domains with less common TLDs:

• ".org" extensions are more appropriate for organizations without a profit motive, such as museums or charities.  Two recent large .org domain sales are Provider.org ($2,500), and Partnership.org ($5,000).
• ccTLDs are especially appropriate when the site’s content is specific to that country (a consumer in the U.S. is much less likely to do business with a company with a “.co.uk” extension than a company that has a “.com” extension but is based in the U.K.).   However, as mentioned earlier, you may very well find the perfect name for your website with the ccTLD for your home country, even though you company does business worldwide.   Some recent ccTLD sales are HotelReservations.us ($2,000), Food.de (Germany, $5,000), and Teens.ca ($4,300).
• As mentioned above, other gTLDs such as .net, .biz, .info, .mobi, or .name can be less effective than a “.com” domain as the former could easily cause your site visitors to be misdirected.  However, many of these domains are still very effective and command great value.  Here are some recent sales:  Camping.info ($28,000), Career.net ($52,500), Traffic.biz ($8,000), Invest.mobi ($22,500).   For a better idea of prices, compare these large sales with more manageable ones:  ElectronicPayments.net ($3,300), HealthFood.org ($3,500), Unity.biz ($4,000), Won.info ($1,550), Antennas.net ($1,100), and Pink.mobi ($5,000). 
  
  Companies commonly use the strategy of buying all TLDs for their domain to avoid any confusion among TLDs, and to prevent brand dilution.  This is especially important for larger companies or organizations which do not use the .com TLD for their domain.  For example, BeautifulPeople.net uses the “.net” extension because the website creates a “network” of (beautiful) users.  However,  BeautifulPeople.net can still be accessed at BeautifulPeople.com.  Similarly, CraigsList.org can be accessed at CraigsList.com.  When starting a new business, providing your budget is sufficient, it is generally recommended that you purchase the “.com” as well as the “.net” “.org” TLDs.  Larger companies (for example, Google) will tend to acquire all TLDs, including all ccTLDs, which may be developed into a site targeted at that country's market, if it is significantly different from the global market.