mongoskin + connect-mongodb

app.js

var mongo = require('mongoskin')
   , db = mongo.db('localhost/collection')
   , mongoStore = require('connect-mongodb');
 
//...
 
db.open(function(err, db) {
    app.configure(function() {
        //...
        app.use(express.cookieParser());
        app.use(express.session({
            cookie: {maxAge: 60000 * 30},
            secret: 'foo',
            store: new mongoStore({db: db})
        }));
        app.use(app.router);
    });
});