gtorrecilla. What do you think of this? Its not the best by line count, but I believe it finds the 2nd largest within O(n).

max = max2 = -100 - int(raw_input())
nums = map(int,raw_input().split(' '))
for i in range(len(nums)):
    if nums[i] > max2:
        if nums[i] > max:
            max,max2 = nums[i],max
        elif nums[i] < max:
            max2 = nums[i]
print(max2)