Wordfence - Comprehensive security plugin for WordPress.
Virusdie - All-in-One cloud-based, simple, powerful and gorgeous website security tools built for everyone.
iThemes Security - Security plugin that provides over 30+ ways to secure and protect your WordPress site.
Sucuri - Website Protection, Malware Removal, and Blacklist Prevention
NinjaFirewall (WP Edition) - A true Web Application Firewall to secure and protect WordPress.
CloudFlare - Cloudflare is a global network designed to make everything you connect to the Internet secure, private, fast, and reliable.