Obfuscated Python
For those who still think Perl is the only language you can write obfuscated one-liners in:
cmath.sqrt((reduce(operator.add, [i**2 for i in l], 0)-(reduce(operator.add, l, 0)*reduce(operator.add, l, 0)/len(l)))/(len(l)-1))
Calculates the standard deviation for the values in a given list l.