Tools we frequently recommend:

• DBAN
• Fail2ban
• IPset
• Lets Encrypt"
• ModSecurity
• OpenSSL
• RRD Gallery
• Stunnel
• VeraCrypt

Websites we like:

• Infosecurity.us
• EFF
• Schneier on Security
• Krebs on Security
• The Register : Security
• OWASP
• Packet Storm
• Wired Security
• XKCD

Contact us if there's anything specific you're looking for.