At this point is spring, it is mating season, couples are making nests- they might like something in your house that might attract them to maybe use, especailly if there are plants in sight.
If you want to scare them away, go to your local hardware store, like Home Depot, and get a large plastic owl. Perch it on an outside ledge outside and this will scare them off.
If you have a water source around your home (like a birdbath) move it to one of the sides of the house that you would perfer them to be. Put up a nest box and an easy to get to bird feeder, and they will be more apt to hang out where the food is.
One thing I have found useful is to put up one of those bird feeders that attatch to your window. They do not look nearly as tacky as one of those out-of-season window clings, and it is not like an owl or hawk shape that will scare them away. This has been a major benfit on the flip side, to us as well. You can watch them using the feeder.
Another idea, look into those breeding boxes you can put on your window that is backless. Once the robins see the "territory" is occupied, they will stay away from the window, and there is a good chance you could have a family of robins nesting, and you can see the fascination of the circle of life :)