Black Swan is still his best in my mind, but the Bed of Procrustes can be a nice entree; aphorisms were the original tweets, and can be consumed as such. Then I'd jump into Fooled By Randomness, and finally Antifragile (which is the weakest of them...truthfully I think the entire book could have been a chapter in Black Swan, but I'm glad he wrote it all down anyway).

All of his books have been worthwhile in some way. "Fooled by Randomness" is a great place to start. Its effect of exposing the lack of objectivity in many commonly-accepted beliefs that rely heavily on perceived cause and effect can add maturity and humility to your own worldview.

Ironically, my only complaint might be that Taleb seems to get a little more self-congratulating by anecdotally revealing the lifestyle he is able to enjoy as you progress through his series of books. Perhaps this is more of a style device to broaden the books' appeal.

Whatever the case, the perspective you can gain from his writing is worth the time.

The one you really want to read, Taleb won't let you - the actual returns from his funds.