Consider these free options to harden your linode servers.

IP Tables GUI ConfigServer Services (standalone and webmin)
http://configserver.com/cp/csf.html

DenyHosts (auto-ban SSH attacks)
http://denyhosts.sourceforge.net/

Fail2ban (Harden Apache/FTP/MTAs)
http://www.fail2ban.org/wiki/index.php/Main_Page

PortSentry (works with IPTables)
http://linux.sys-con.com/node/32843

Tripwire (ubuntu) - baseline CRC file checking
http://netwizards.co.uk/installing-tripwire-on-ubuntu/

TIGER (The Unix security audit and intrusion detection tool)
http://nongnu.org/tiger/

PHP Hardening
http://www.hardened-php.net/suhosin/

_________________
Faisal Humayun

And how much resources do all those "required" addon's use up?

What about just uninstalling FTP and disabling password-based SSH logins? You can't beat that.

Other tools you listed may be useful for some people, though.

Note that the core features of Suhosin are already part of Debian and Ubuntu's PHP packages. The rest of Suhosin's features can be enabled by installing php5-suhosin, though it's usually unnecessary.

As usual, the most important thing is to know when you need a tool, and to use the tool properly. People who think that they'll be safe just because they installed a certain program are even scarier than the bad guys themselves.