"Structural Corruption" shows a perfect example of why "Numb3rs" is in a whole other class compared to other prime-time crime series. We've got strong characterization, a mystery that is more complex than it first appears, and the family dynamic among the Eppes men.
A suspicious suicide sets Charlie's investigative mind working, and for a change he goes to Don for help in trying to find out why (and if) a student took his own life. I was surprised to see where the story went (the rebar construction, etc.) and found it to be a refreshing change of pace from most murder/rape of the week shows. The ending was particularly powerful, as the truth about the death comes out. David Krumholtz can toss the math jargon off with aplomb, but he especially shines in scenes when the clinical, detatched Charlie gets bowled over with an emotional truth.
Plus, the fantastic (and usually sorely underused) Judd Hirsch gets a chance to shine as he prepares for a date (and tries to weedle Don and Terry into one as well). Sabrina Lloyd and Rob Morrow had such great chemistry - I would have loved to see their relationship grow and develop over the course of the series. It's too bad she left the show just as it was starting to get going.