In England, there is a series called "Spooks." When it plays here on BBCAmerica, it is called "MI-5." MI-5 is the British equivalent of the FBI and MI-6 is their CIA. For example, James Bond works for MI-6.
There are currently 6 seasons, which is roughly 62 episodes. I watched the first 4 seasons on Netflix Instant. I currently am in the middle of season 5 on DVD and looks like their is a bit of a wait for season 6.
The show is amazing. It is well written, well acted and I've found myself holding my breath on more than one occasion. There is a real sense of danger because they have no hesitation in killing off characters when the plot line calls for it. The first two seasons have a real sense both plot and characterization. Season three and four focused more on plot and now season five seems to be back on track.
I highly recommend checking out this series. There isn't a week episode so far which is impressive that it can keep the same level of intensity episode after episode. I also feel like they show the real wear and tear of being a spy would have on the characters over time.