Clark running into a tornado in the Smallville S1 finale. Maybe the only moment I can think of offhand in which he really charges into danger unsure of whether or not he can take it. But catching a falling 747? About as daunting as a medium-level workout.
My favorite Smallville feat is when he cleans the house at superspeed after a party, before mom and dad get home.
In the movies, I really like the Action Comics #1 moment when he has the car over his head.