The popular site is called Craigslist, one word. If he had called it Craig's List, then yes, you would be able to make your own. It's your given name and a common English word. Not trademarkable.
It is not true that you have to combine things as a novel compound word (as with 'craigslist' and many other tech firms) in order to obtain trademark protection. Common names and plain words/phrases can be protected too, within a well-identified field of use, by either formal registration or force-of-use-over-time.
"Craig's List", in the field of an online listings site and community, is just as protectable as the smushed-together version. And, by risk of confusion with 'craigslist', the two-word version is now just as excluded from others' use as if 'craigslist' itself were named "Craig's List".
Even if your name is 'McDonald', you won't be able to open a "McDonald's" hamburger chain. If you wanted to sell cash registers worldwide, you couldn't start an "International Business Machines". You couldn't even get away with "Jonathan's International Business Machines".
In the legal terminology, a trademark like either 'craigslist' or "Craig's List" would be considered a descriptive mark that has acquired secondary meaning via use, such that the consuming public identifies a mark with a particular producer. It now doesn't matter if your name is Craig and you have a List. If you name a business that and people are confused because the field of use is similar to those for which Craiglist is known, Craigslist has a valid case against you.
The Wikipedia article (http://en.wikipedia.org/wiki/Trademark) also highlights that "The test is always whether a consumer of the goods or services will be confused as to the identity of the source or origin."
Another example of the primacy of the liklihood-of-confusion standard is the following guide page at the USPTO:
