Choosing a smart password

Solution 2: Use a password with a mix of letters, numbers, and symbols

There are only 26^8 possible permutations for an 8-character password that uses just lowercase letters, while there are 94^8 possible permutations for an 8-character password that uses a combination of mixed-case letters, numbers, and symbols. That's over 6 quadrillion more possible variations for a mixed password, which makes it that much harder for anyone to guess or crack.

from: http://gmailblog.blogspot.com/2009/10/choosing-smart-password.html