Nodemon is a utility that will monitor for any changes in your source and automatically restart your server. Perfect for development. Install it using npm.
npm install -g nodemon
Once installed, instead of node app.js use nodemon app.js . It will save you a lot of time in the long run, because you won't need to manually restart the server each time you make a change.
edit: These days I'm using a ever so slightly more popular PM2.