Wordfence - Comprehensive security plugin for WordPress.
Acunetix - Audit your website security and web applications for SQL injection, Cross site scripting and other...
iThemes Security - Security plugin that provides over 30+ ways to secure and protect your WordPress site.
PracticeProtect - Network security & identity management
NinjaFirewall (WP Edition) - A true Web Application Firewall to secure and protect WordPress.
Intruder - Intruder is a security monitoring platform for internet-facing systems.