Sometimes for indoor shots i use a external flash, mainly to bounce off the ceiling. Brightens up the whole picture, no harsh shadows, room background is intact, and better depth of focus due to smaller apertures.
C'mon, need to be realistic here, don't expect too much from the on-board flash of any DSLR.
With a Guide Number of 12-13(ISO 100/m) don't expect miracles. The flash coverage is supposed to cover the angle of view of an 18mm lens but light fall off and even coverage is always going to be an issue. Plus as power is drawn from the camera's batteries, instant recharging is never going to happen.