I would have to say the most interesting meme for me would be this:

"I exist"

On this one meme balance precariously things like "I want", "I am", "I own", "I believe" and so on. This makes it probably the most important meme in our perception of the world. (The other important one being "the universe exists", or perhaps "existance exists".)

The existence of self is indeed questionable. Have you ever looked upon the rest of the universe, and wondered what makes you so seperate from it? The meaning of 'I' is not clear or well defined; what makes me think I exist at all?