LastPass is a secure vault that stores and manages all of your passwords. The idea is that you'll only have to remember one single password -- the one for LastPass. It installs as a browser extension on Windows, Mac, and Linux. There are also mobile apps available for iOS, Android, Windows Phone, and Blackberry.
After LastPass is installed, it will prompt you to save new sites to your vault as you visit them. Once you have sites saved in your vault, LastPass will automatically fill out the username and password fields when you go to login. If you're signing up to a new site, LastPass will generate a secure password for you. It gives you control over the length of the password, what types of characters will be used, and more. It also can store secure notes and credit card information. Your information is then synced to all of your other computers and devices that have LastPass installed.
LastPass has several security options including multi factor authentication. This would require you to have a smartphone, a printed grid, or an actual key to get into your account. You can set it up so that it won't allow logins from other countries, and you can have it only allow logins from trusted computers and devices. LastPass will also audit all of your passwords and tell you if you've used the same password twice, or if you have a weak password that should be changed.
LastPass is not only convenient -- it's very secure too. It's been vetted by security expert Steve Gibson, and it uses a "trust no one" model. This means the data is encrypted in such a way that only you can see your data. Not even LastPass or the government could access it.
LastPass is a fast, secure, and convenient way to handle all of your login information. The desktop version that runs in your browser is free to use, while the mobile app is a $12 a year subscription.