What Domain Name Should I Choose?
Back in the late nineties, it was customary to purchase domain names in sets - for example, our ficticious skate shop 'Wheels of Steel' would've bought wheelsofsteel.co.uk for their main site (as they're UK based) and wheelsofsteel.com which would point all traffic to the co.uk site.
The idea behind this thinking was to ensure that competitors or similar companies could not purchase a site with a similar name to yours, and it also caused a rise in a number of people purchasing domain names that they knew would be wanted by larger companies - such as Boots pharmacy or Cocoa Cola.
Google 'trusts' older domain names
The practise of purchasing all of the possible variations of a domain name is not a bad idea in terms of website optimising and increasing your traffic, but you need to bear in mind that it does create more hard work for you. There are also several things to bear in mind here; Google 'trusts' older domain names, so once you have your domain, stick with it for as long as possible - this makes things easier for not only search engines, but also for your customers to find you again. There are also websites which will sell domain names that have expired or 'dropped' -you may consider one of these try and find one with what you sell in the name.
This means that as well as your Wheels Of Steel.com and .co.uk sites, you might purchase domains like buyrollerskatesinleeds.com or buyrollerskatesonlineinyorkshire.com and try using those to link back to your main site. This is called 'mirroring'. The basic rule is combining a .com and a .co.uk is, in most cases, fine and dandy, but when you start getting many domains with search term titles to point at your main site, Google will find you out and thus negatively affect your ranking.
Something else to consider is where are your customers? Do you want to sell internationally or to specific countries? If so check where your site is hosted and also consider buying the domain name for the country you want to sell to. For example, if Wheels Of Steel sold to Germany then buying the domain name wheelsofsteel.de will help you with your search engine rankings in that part of the world.