1) Norton DNS: https://dns.norton.com/dnsweb/dnsForHome.do
It's free, filters out bad URLs, is compatible with all AVs and takes no system resources.
2) Sanboxie: Sandboxie - Sandbox software for application isolation and secure Web browsing
It's free (although a lifetime license is available that has a few more features) and is compatible with all AVs. Sandboxie will place your browser in a virtual sandbox making your system almost bullet proof from online threats. It takes a little bit of time to get used to it, but there are plenty of tutorials on YouTube that will help you learn fairly quickly........ But be warned, once you get used to it, you'll want to dump your AV altogether.
3) Novirusthanks EXE Radar Free/Pro: NoVirusThanks EXE Radar Pro - NoVirusThanks
They offer a free and paid version (lifetime license). It is an anti-executable that prevents .exe's from running unless you alow them once, or whitelist them forever. It is very easy to learn, and takes few system resources.
4) Hitman Pro & Malwarebytes: HitmanPro 3 - SurfRight Malwarebytes : Free anti-malware download
Both are free on demand scanners and are considered among the best available.