http://www.castleproject.org/monorail/
Look at the description:
"Monorail.js will never force you to install anything not needed for your project. The goal is to use what you need."
Plus, it's definitely lighter than express.
I think if I were to use a node MVC framework built on express, I'd go with Matador: http://obvious.github.com/matador/
I've also found Grasshopper to be a great one: https://github.com/tuxychandru/grasshopper
http://www.castleproject.org/monorail/