Since you are not supposed to use the same one for all your sites, e-mail accounts and software as well as online banking you either have to remember them or er..write them down!
Enter Roboform. A really cool tool which will store all of your passwords in an encrypted file which you protect with a master password.
The master password can never be recovered so make sure you choose one you will definately remember.
All you need to do is enter the master password once and then Roboform will fill in any passwords via the click of a button. You can still manually enter the ones you don’t want to store such as online banking.
Roboform works on PC, Mac and mobile devices or you can have a version which works across multiple platforms and synchs up.
If you find yourself being frustrated at having to remember multiple passwords then for under thirty bucks, Roboform may be a lifesaver for you.