I'm putting together a presentation to talk about and demo node.js to client-side JavaScript developers. The language concepts and syntax are not an issue for them, so instead I'd like to get right into things and show off node's abilities that differ from client-side scripting. There are numerous modules available in the NPM registry and many people have much more experience with the registry than I do.

I'm looking for a selection of node modules based on recommendations from your experience that show a variety of uses for node that are practical, broadly useful and can be demonstrated with a small code sample without requiring much domain knowledge on behalf of the audience. Neat and impressive is good too - I can throw in a couple of shock and awe items for cool factor.

To be fair, top-voted answers will get most consideration for inclusion. My hope is this will result in a well-rounded demonstration of node technology.