I am a bit of a connoisseur of apocalypse movies, television shows, and books. I love the stories about how society/humanity gets destroyed and about how the people left behind have to begin to deal with the "restructuring" of their problems.
Warning! I might have a few spoilers here that some folks would not appreciate!
Contagion stands out as a bit of a spin on the subject; the whole movie exists in the space between Day 0 and day 200. Its the story of the decline - not just the story of the aftermath. What's more is that the movie does an amazing job of creating a reality that we all live in everyday. Which it then summarily disassembles right in front of us causing us to question the assertions we work off of everyday. The movie's virus kills in 4 days and can be transmitted in many, many ways. Making it virtually impossible to remain uninfected if you have been in contact with someone who has. All of the key reactions you can wonder about have been covered, the CDC, government, blogosphere, facebook, municipalities, local neighborhoods - the story is very thorough in leaving no stone unturned from an apocalypse geek perspective.
The real genius of Contagion is the presentation of the horror angle - it could really happen; and Contagion tells a story about what it might look like if it did, and it looks very scary. It is expertly directed and performed by an amazing cast of people who make it look effortless. Finally - I think you should see it in the theatre so that you get a real feeling for the scale of the epidemic. The small screen may take a little bit away from that...