If you're security conscious then you'll probably want to have a different password for each of those online services. Remembering all those username and password combinations, and which combination goes with which can be quite the challenge.
That's where KeePassX comes in handy. It's an open source password manager that securely stores your passwords for easy retrieval. You'll need to manually enter usernames and passwords for your online accounts, and you'll need to remember to keep those stored passwords up-to-date, but you'll only need to remember just the one master password to have access to all your accounts once everything's setup.
|KeePassX in Software Center|
|Creating a key file for KeePassX|
|Adding an account entry|
KeePassX even provides buttons to copy an account's username/password to clipboard so you don't even have to type the password manually. If you still prefer to do so, just click the button with the eye icon to reveal your password when you need to see it and click once again to hide it.