The site node frameworks will give you a list of available frameworks. I'm quite new to NodeJS but what I discovered the hard way is that in the nodeJS ecosystem, the most popular libraries are based on Express and/or Connect (Express being itself build on top of Connect).
So if you choose another framework, you could be stuck like I was, when trying to integrate some popular libraries like Passport for authentication. Moreover Express popularity will allow you to find many tutorials. That's why I would recommend you to use it.
update: you may discover popular modules for node on NodeJS Modules