These. And pretty much for the same reasons (although I get my news from The Daily Show instead of Letterman).
Daily Show-As mentioned before, this is how I like to keep up.
Late Night w/Conan-The silliness is what makes it great. Conan is my favorite late night host.
The Soup-Joel McHale is awesome. Their regular bits such as "Chat Stew" and "Reality Show Clip Time" are amazing. Bad TV makes good TV.
Saturday Night Live-People say it sucks anymore. I disagree. While there are often terrible sketches, the majority of the show is genius.
That's about it.