First letter frequency for en Wikipedia, articles which aren't redirects only. 432891 of those on 17 December 2004.
select left(cur_title,1) as a, count(*)/432891*100 as b from cur where cur_is_redirect=0 and cur_namespace=0 group by a order by b desc;
+---+------+ | a | b | +---+------+ | S | 8.34 | | C | 7.43 | | M | 6.63 | | L | 6.59 | | A | 6.48 | | B | 5.96 | | T | 5.90 | | P | 5.40 | | H | 4.31 | | R | 4.24 | | D | 4.00 | | G | 3.89 | | J | 3.70 | | F | 3.45 | | E | 3.40 | | W | 3.32 | | N | 3.04 | | K | 2.40 | | I | 2.24 | | O | 1.94 | | U | 1.86 | | V | 1.49 | | 1 | 1.44 | | Y | 0.59 | | Z | 0.43 | | Q | 0.34 | | 2 | 0.27 | | X | 0.18 | | 3 | 0.12 | | 4 | 0.10 | | . | 0.08 | | 5 | 0.07 | | 7 | 0.06 | | 9 | 0.06 | | 8 | 0.06 | | 6 | 0.05 |