Seth brings up a good point in his recent blog post about how NOT to start conversations. It's a basic tenet: don't give them the chance to use one-word answers. "How are you?" is met with "Fine" - semantic content, nil. "Wow, where did you get that great necklace/briefcase/llama?" is usually a better way to actually make a connection, to show the person that you actually see them, and are making a connection.
Part of my duties here include de facto receptionist. I never say "May I help you?" - I know that I can, I ask "How can I help you?" or, if I'm feeling jovial, "Hey there. What can I do ya for?" It breaks the mood, it makes them think about complete sentences for an answer, and it's just plain fun to see them thrown off their stride, expecting a grumpy tech guy and getting affable ol' me instead.