How can I flatten my stomach quickly?

I’m trying to flatten my stomach so I can improve my appearance, and have been trying various exercises from crunches to situps, and have seen absolutely no results whatsoever. I’m alerady losing weight, but I need to tone my stomach, and have very little time that I can devite to exercise and get discouraged very easily unless I see results fairly soon. Can someone please help me to get quicker results and to keep motivated and on track?