When you create your new website give yourself ample time to research and purchase a domain name that will help your business from the start.
When looking for a domain name the .com's are preferable to all other suffixes. Most any decent .com is already taken but with the explosion of domain suffixes that has become available for you to purchase, you could still purchase a domain with any number of other suffix. So while yoursite.com is taken you can still purchase yoursite.cc or yoursite.bz, the biggest drawback with this is that people surfing the web are accustomed to .com names.
Search engines (SE's) look for relevancy when ranking sites in their directories. If you have a site about widgets and widgets.com is taken, but you own widgets.bz, it will be a lot easier to rank widgets.bz then say fredswidgetcompany.com for widgets. The downside to this is that while it will be easier to rank in the SE's for widgets, web savy people are going to trust sites with top level domains (such as .com, .org, .info, net) then those that don't have a top level domain.
If you are creating a personal website this is not all that important, however if you are creating a new site for your business a top level domain is essential, .com is optimal for this. The reason behind this is that it is easier to remember a .com and they are deemed more trustworthy then their counter-domains. Simply put if your new site is for a business then a .com is essential. It might take more work to rank high in the SE's, but over a period of time it will be well worth it.
Keep your domain name relevant to your company! Let me state that again. Keep your domain name relevant to your company! If the domain name you want is unavailable, be creative. Back to the widget example, widgets.com is unavailable. You could always try singular or plural versions of the name. If both of those are unavailable and you are a regional company, then try adding your location to the domain name. Midwestmidgets.com or ohiowidgets.com, this will help if people are searching for your product in a certain region. If both of those are taken then I would try the name of the company, fredswidgets.com. or fredswidgetcompany.com. I would still purchase the name of your company either way and have them redirect to the other domain name. If you can avoid it, do not purchase names that have two or more words that start and end in the same letter like samsstuff.com or fireworkssale.com. If you are in the position to purchase a domain like this try to purchase both variations of the name with and without the double letter.
If you still can't find a domain name you want, or you are stubborn and want a domain name that is relevant, you could add a hyphen to the domain name if your keywords is more then one word. This trick can work with as many words as you like widgets-sale.com, widgets-for-sale.com. I have also scene this work for breaking your keyword midword wid-gets.com. Apparently SE's don't recognize or validate hyphens in domain names or if they do the ranking is slightly different versus non-hyphenated domains. The big drawback to breaking your domain midword is that while this may help for SE's, you won't be winning any points with your customers.
Then there is adding numbers to the name, and this is only used as a last resort. If you are forced to use numbers in the domain, try to keep the numbers relevant and never at the beginning of the domain if possible. If you can, try to use "2" as to or 4 as "for" in the domain. This also works for r as "are", u as "you", b as "be"...
