It was Fooled by Randomness. (Randomly enough I was reading that book for the first time yesterday)
I just read it a couple of months back because I figured I probably owed reading some Taleb as back table stakes for all the hours I've spent reading HN (and SSC). Picked Black Swan because it seemed to be the most well known and I've never liked jumping into a series with the most recent release. I enjoyed it, will read more of him, but haven't yet.
Do you have an order recommendation?
If you've read the Black Swan already that's fine. My recommendation is mostly addressed to those who have read neither.
I highly recommend reading Antifragile next though. It's fairly different from the other two and extremely interesting; probably one of my favorite books.