Sometimes you would like to check passwords to be conformant with some rules. At least one digit, one letter is a common one. Here is the regexp for this:

(?=.*?[0-9])(?=.*?[A-Za-z]).+

Allows special characters and makes sure at least one number and one letter.

Update:

(?=.*?[0-9])(?=.*?[A-Za-z])(?=.*[^0-9A-Za-z]).+

Demands at least one letter, one digit and one special-character. The first one does not demand special chars, only allows them.