Ask HN: Should I register several TLDs for our domain name?
Is registering the .org, .info, .mobi TLDs etc. and all the country TLDs necessary for a start up?
Beyond that, if you are in a certain locality and you plan to roll out with local press support it can't hurt to have your local tld version as well.
If you want to roll out customized versions per country then you may have to go further, lots of countries have some pretty weird rules about registration though.
Remember to get yourself a trademark issued too!
But of course it's not a perfect world and if you dont snap up the others chances are domain squatters will wind their way in.
.mobi and .tel are probably a waste of time. I would only recommend you register ccTLD's for the country you plan to launch in and/or the country you are based in. If you are a truely global (i.e. web based) type company, then just the first five are probably fine.
(disclaimer, I work for a domain registrar)
A couple of the others might be valuable, but moreso other country domains (someone else mention the .co.uk and such already). I just wouldn't worry about the seldom used variant tld's myself.