I store mine in keepass. Its a free tool that provides an encrypted database to store all your login credentials in.
Usefully it can also generate complex passwords for you, and you can copy and paste these into appropriate locations as and when required.
There's an interesting clip on u tube about how easily non complex passwords can be broken with the right tools, suggests that passwords need to be 15 characters plus (and preferably pass phrases) to get near being secure.
See it here
SecurityWise: How Password Crackers Work - YouTube