I find it fairly easy to turn an "atheist" into, at the very least, an agnostic with three quick questions.
1. Do you believe the universe is infinite?
Atheist: yes
2. Do you understand the 2nd law of thermodynamics?
Atheist: Yes or No (either answer will do)
(explain: The Second Law of Thermodynamics states that the state of entropy of the entire universe, as a closed isolated system, will always increase over time. The second law also states that the changes in the entropy in the universe can never be negative.) In laymen’s, energy, much like a car filled with gas, will eventually run out. So if the energy will run out, it must of started somewhere?
3. So if you are going on the theory that the universe is infinite, then the LAWS of thermodynamics are false. And if the laws of thermodynamics are false, then the laws of gravity also do not apply. You believe in the gravity right?
Atheist: well....Yes.
Response: So if you believe in the laws of the universe that clearly state the universe is NOT infinite, then you have to come to the logical conclusion that something, somewhere, at some point, started the universe!!
And BOOM!! You have got an atheist at least starting to think about his/her choice to have faith in nothing. I personally don't have enough faith the be an atheist.