It is almost impossible completely "lock up a brand" by buying it for every top level domain. There are hundreds of top level domains with new ones coming online all the time. Only well funded companies have enough money to spend on that.
I have traditionally purchased the
.net together. But at this point I'm questioning the necessity of that. It is unlikely for somebody else to create very much confusion by putting up a site on another top level domain.
- Google is very good about ranking the original site with the best content in the first position of search.
- If you trademark your name, you will have trademark law on your side and you can wrest domains away from squatters using trademark law if you really need to.
If you are setting up the site on something other than a
.com, I'd purchase the
.com as well because it is often the default for type in traffic. Otherwise, I wouldn't bother trying to get your domain name on lots of different TLDs.