OMG! My husband and I were just talking about Sesame Street earlier today. I lived and breathed Sesame Street as a kid (even had the 1979 Sesame Street lunchbox, now being sold on eBay for good money!) and I have to say my favorite character of all time has to be Ernie. I just can't get enough of that guy's craziness. He's so funny being paired up with Bert as his best friend 'cuz they're sooooo very different.
There's one skit they did way back that has to be my favorite too. I don't remember the exact dialogue, of course, but the basic premise was Ernie had 2 cookies (one for himself and one for Bert) and 2 glasses of milk (one for each). Apparently the sizes of the cookies were different so Ernie was trying to chew the cookies down to an equal size so he and Bert had the same. The same thing went with the milk; Bert's glass started out with more so Ernie drank some of it, then his glass had more, etc., etc., etc. I'm sitting here laughing just thinking about it.
Grover comes in a very close second too. I have a cousin who does the perfect imitation of Grover doing his neeeeear and faaaaaar skit. I love it!
Sesame Street played a huge part in my childhood and I'm looking very forward to passing that on to my own kids. I've caught an occasional episode of SS here and there over the last few years and it's also funny to watch them as an adult and realize that some of the humor was made to be funny so that only adults can get the joke. I'm assuming that's for the parents that are watching with their kids, just so they're not bored to tears.
ETA: I was just looking at the yip yip martians clip and noticed in the bottom right hand corner it said NOGGIN. My kids are only 1 year old and we have that channel on all day long, just playing in the background. Of course my kids are too young to actually sit and pay attention to TV but, boy, does the music sure catch their attention!
Also, as far as Jim Hensen's other shows and characters, I think one of my other favs were the Swedish Chef on the Muppet Show and the grumpy old hecklers.