Don't ignore a small crack in the windshield caused by a flying stone - it can spread out to a wider area of the windshield and costs you $$$.
You don't have to take my word for it: http://www.wikihow.com/Repair-a-Windshield
Instead, take your car to United Auto Glass - it only costs $25 for a small dent, and that's exactly what I did!
Honest and fast service.