Prestomap and Jobslinger are where the MSC's post the shops they have difficulty filling. It's good for a newbie to find companies that are shopping close to them and to start out with the fun assignments.
I use PrestoMap on my main computer with a hires screen and can back the map out to show every advertised job for a 50 mile radius at once. It is not just for mobile at all. I find it better than JobSlinger for navigation and obviously the map really helps when building a route. It's always worth taking a look before you head out the door for another shop to see if you can self assign something along the way.
The plum assignments are posted only on the internal Sassie shop board and are immediately snatched up or applied for by everyone who is not out of rotation guidelines.