Most of the episodes this season do a nice job explaining mathematical concepts including several relating to theoretical computer science (see below), though the connections between the math and the plot get more and more tenuous.
A couple of Numb3rs related web sites give more details on the mathematics described in the show. Texas Instruments created a site giving high school level descriptions and activities on the topics discussed in the show including Voronoi Diagrams, Entropy, Eulerian Tours, Steiner Trees, Error-Correcting Codes, The Art Gallery Problem and Pseudorandom Numbers. Also, a Northeastern professor writes a weblog giving more detailed mathematical explanations of the topics on the show.
In my favorite episode of the season Convergence, a rival mathematician gives a talk finding a hole in the proof of the Epps Convergence, Charlie's best work. This causes Charlie to go through an introspective phase questioning whether his FBI work keeps him away from doing his real research as a mathematician. He considers the importance of being a mathematician while being part of a larger world, philosophical issues that many real mathematicians also contemplate.