The clutch debate has been going on in baseball for some time now. There are, as with any controversial topic, the staunch believers, who maintain that a hitter's ability to perform at a higher level in clutch situations is a repeatable skill somewhat indicative of his overall quality and value to his team. The other side, mostly the sabermetric community, has looked into this and repeatedly failed to find evidence of such a relationship. Players can perform better in clutch situations during any given season, as they can for any other small subset of plate appearances, but until there is evidence of that being a repeatable skill, I don't believe it is enough to qualify them as a clutch hitter.
That being said, it's still noteworthy to know which players have been at their best when it matters most. We can classify these situations using Leverage Index, which essentially measures the range of the possible changes in win expectancy for any given plate appearance. In a tie game in the top of the third inning, the Leverage Index is low; down one run in the bottom of the ninth, it's high. My analysis used the FanGraphs definition of high leverage, which is any plate appearance with a Leverage Index of 2.0 or higher, or about 10 percent of all plate appearances. Unsurprisingly, most of the top high-leverage performers are there because they're good overall hitters, although there are a few surprises among them as well, as you'll see.
Steven Souza, Tampa Bay Rays: The Rays are still in the hunt for that second wild-card spot in the American League, and Souza is playing a big role. In high-leverage situations, he has been up to the plate 68 times and is slashing .304/.426/.500, driving in 23 runs and hitting three home runs. The one downside is that he's still striking out a quarter of the time in those plate appearances -- the second-highest mark on this list -- but given the production he has provided during the most pivotal situations of games, he can probably continue to get away with that.