I'm guessing you have already seen Samuel Jackson's iconic performance in Pulp Fiction (1994). He is among my favorite actors but I do wish that he did not take on so many minor or supporting roles instead of searching for lead roles because he has a lot to offer (as Genesis said in this thread, he has strong presence). For this reason I would suggest you check out Coach Carter from 2005, as it gives Jackson the opportunity to build a character with more depth and screen-time, allowing the viewer to build a deeper connection and taking Jackson seriously (unlike snakes on a plane).
On a similar note, if you are truly a Samuel Jackson fan, you should check out Lakeview Terrace (2008), in which he is also the lead and is given a lot of freedom to build his character over the course of the movie. It is not blockbuster or even well-rated on imdb (6.2), but I like that it gives a setting for Jackson to show his interpretation of a character with an unpredictably crazy and scary side.