Best Free Anonymous Surfing Service
JonDo (previously known as JAP) is my top choice and a Java application that performs the role of a local (PC based) proxy server that redirects browser requests via the JonDo network. This allows the user to configure their choice of any browser rather than requiring a change to Opera. (Review)
Best Free Antivirus
ClamTK Virus Scanner is a graphical user interface for ClamAV and designed to be an easy-to-use, on-demand scanner running on Linux systems.
I thought Linux doesn't need antivirus protection?" It's true that you may not need it, but this program is more geared for users interested in scanning files prior to sending them to users of other operating systems than Linux.
Best Free Firewall
Gufw is a graphical user interface for UFW (Uncomplicated Firewall), and as the name implies, an easy-to-use firewall for Ubuntu, Linux Mint and other Linux systems, with support for setting up rules such as allowing or blocking applications, incoming and outgoing services, common P2P or individual IP/ports, with options for logging and showing notifications.
Firestarter , a complete firewall tool, allows for users to create a firewall with a wizard, open and close ports with a few clicks, completes with a real-time hit monitor.
Best Free Internet Safety Check
WOT , fastest ratings, uses green/yellow/red ratings and 'people' reliability icons, multiple rating categories to help you evaluate websites, fantastic warning screen to empower users to avoid potentially bad websites before interacting with them. (Review)
Best Free Password Manager
KeePassX , you just need to remember one single master password to access many user names, passwords and other private information saved in one single database. Features include defining titles and icons, grouping and sorting entries, and generating secure passwords.
The database is encrypted either with AES or Twofish encryption algorithm using a 256 bit key and uses a file format that is compatible with KeePass Password Safe for Windows.