Non locking carabiners come in three different categories:

The Gate openings are the same here as they were with the quickdraws. Main categories to look out for are straight, bend or wiregate carabiners. 

The main thing to keep in mind here is that non locking carabiners should NEVER be used as belay, rappel or anchor devices. They are essentially carry tools and should not be used for anything else (except quickdraws).