Find The Least Common Characters Given a string, find the 10 least common alpha-numeric characters within that string.

Output should be formatted with numbers left-padded with spaces so they look like this:

e:      1
t:     16
c:     42
b:    400
z:  50000
a: 100000


Use this to test your program: here

Output for test case:

j:  2
x:  3
q:  9
k: 32
v: 67
c: 73
w: 79
f: 93
b: 94
p: 96


Shortest code wins. You can submit a program or a function.
Mathematica, 102 93:  

v2:

  Grid[SortBy[
             Tally@StringCases[ToLowerCase@#,x_?LetterQ:&gt;x&lt;&gt;":"],
              Last@# &amp;],
      Alignment-&gt;Right]&amp;@s


v1:

TableForm[
         SortBy[Tally@StringCases[ToLowerCase@#, x_?LetterQ :&gt; x &lt;&gt; ":"],
                #[[2]] &amp;], 
         TableAlignments -&gt; Right] &amp;