Yesterday I mentioned the .uk top-level domain (TLD), which becomes available without restriction soon. But there are hundreds of others too now. Go to any domain name provider and type in your company name. The range will probably amaze you. The question is: do you need to hold some of these, even though you don’t use them?
There are two reasons for holding variations on your main website domain name that I can see. The first is defensive: if you’re bluewidgetcompany.co.uk, there’s no reason why someone with unsavoury motives can’t register bluewidgetcompany.com or indeed any other variation. But is someone likely to? Frankly, unless you’re a household name, I doubt it. And even if they were, they could always find something that looked like your domain name to use.
The second reason for holding a variation on your domain name is probably to cover common mistypings, such as if you use a hyphen in the domain name and want to get people who omit the hyphen to be redirected to the site. That’s not such a big issue nowadays, as it’s probably rarer than ever for people to type in URLs, but for such a small investment, maybe it’s worth it.
So in general, I’d say don’t bother investing in any variations on your main domain name. If you have some already, and aren’t worried about the cost of renewing them, perhaps do so, because many people monitor for lapsed domain names and might find them interesting. But in general, that’s probably all you need to do.