Get list of connected users with Django
You have to consider what exactly means for the users to be "online". Since any user can close the browser window any time and without the server knowing about that action, you'd end up having lots of false "online" users.
You have two basic options:

Keep track of the user's last activity time. Every time the user loads a page you'd update the value of the timer. To get a list of all online users you'd need to select the ones with an activity before X minutes. This is what is done by some web forums.
Open a websocket, long polling connection or some heartbeat to the server. This is what Facebook chat does. You'd need more than just django, since to keep a connection open another kind of server-side resources are needed.
I'm looking for a way to keep track of users that are online/offline. So if I present all users in a list i could have an icon or some kind of flag to show this. Is this built in in Django's default Auth system?
My first thought was to simply have a field in my profiles called last_logout in the models and update it with the date/time each time user logged out. 
With this info and the built in last_login I should be able to make some kind of function to determine if the user is loggedin/online right? 
Or should I just have a boolean field called "online" that I can change when user logs in and out?