Ben Fry analyzes the data from an intelligence test administered to all incoming NFL players and displays the results by position. Offensive players do better than defensive players on the test, although running backs score the lowest (wide receivers and cornerbacks also don't do well). As Michael Lewis suggested in The Blind Side, offensive tackles are the smartest players on the field, followed by the centers and then the quarterbacks.
Malcolm Gladwell talked about the Wonderlic test at the New Yorker Conference and judged it a poor indicator of future performance.