See my list at: My Dream list of "Things" in Priority Order
I also agree on the doorbell, ir sender and receiver and the in wall scene controller (like this: http://www.cooperindustries.com/content/public/en/wiring_devices/products/lighting_controls/aspire_rf_wireless/aspire_rf_5_button_scene_control_keypad_rfwdc_rfwc5.solutions.wiringdevices!whole_home_solutions!aspire_rf_wireless.html ). Actually would be good to have proper scene Managment and device association. Also thermostat schedule management (I know there are projects for that, but it should be part of the app)