A .com suffix is the most famous; it is also the most powerful in terms of eliciting search results. All other things being equal a .com domain will show higher in a Google search result than, say, .co.uk.
Unfortunately all the best .com names have already been registered; worse still some companies and individuals have registered thousands of potentially useful names in order to sell them at a profit.
Other 'powerful' non-geographical domain suffixes are .net and .org although the organisation in charge of issuing domain names (ICANN) releases new suffixes from time to time.
Recently .uk has been introduced in addition to co.uk. Obviously it has one advantage: it is shorter.
And that brings me to another important point: in general terms keep your name short. The longer it is the more chance there is of people not remembering it or mis-typing it when looking for your company. So try to keep it snappy.
If possible limit the name to a single string of letters. For example mossbrothers is better than moss-brothers and certainly avoid moss_brothers.
The exception to this rule is if your business is area specific, in which case having the domain name mossbrothersrichmond will, once again, improve your search rankings if you want customers in the Richmond area. Or, to be absolutely certain, you could purchase mossbrothers and mossbrothersrichmond. The extra annual cost is minimal.
Another approach is to not be so literal; think out of the box. The B&Q company use the domain name diy.com. In part that is because the symbol & cannot be used in a domain name. If you were a roofing contractor based in Richmond you could therefore consider the domain roofersrichmond. That would produce very effective search rankings because those are the words potential customers in your area would type into Google, so you would naturally appear high on any list.
The Domain Names Registry charges roughly £10 per year for a domain. I do not make any administrative charge for arranging it for you. There is simply a 50 pence EFT (Electronic Funds Transfer) charge per bank transaction.
If you do not already own a domain name please allow me to register for you as it can be time consuming to transfer it and the registrar may levy a small transfer charge