Hm. There are av’s designed to work alongside another i.e. Threatfire (so long as it is never registered in the security center), ImmunetProtect, Rising PC Doctor and ClamAV. All others, unfortunately, are not. I read there are a few others in existence but have not found them. You may also try on-demand scanners such as Bitdefender Free, Trend Micro HouseCall, ESET Online Scanner, ClamWin, and Dr.Web CureIt among others.
If, however, these do not fit your fancy, you can try other security tools. Task Manager alternatives such as Anvir Task Manager, Neuber’s Security Task Manager, Glary Utilities’ Process Monitor, Sysinternals’ Process Explorer, Innov-sol’s Advanced Task Manager, Chameleon Task Manager, ProcessLasso (not really an alternative but can function as such), Auslogics’ Task Manager, the open-source Yet Another Process Monitor, System Explorer, Process Hacker, are my personal favorites and often feature security ratings along with detailed information about an item. There is also the popular HIPS software if you’re willing to put up with a few annoyances. There’s the ever-popular WinPatrol, Samurai, PrivateFirewall, and Comodo’s own Defense + (which also functions as a behavior blocker and sandboxing application).
Sandboxing is another popular alternative. Returnil features not only a sandbox, but also an av with it. The more popular Sandboxie is a good choice and the Chromium browser is sandboxed already. Full system virtualizations are also good products. These include Wondershare Time Freeze, Faronics’ DeepFreeze, and Microsoft’s Windows SteadyState.
Other security softwares include Comodo Programs Manager, System restore alternatives such as Comodo’s Time Machine, Wondershare’s Time Shuttle, and Rollback RX.
There are dozens, maybe even hundreds more that could further secure your pc. It’s just a matter of choosing those you are most comfortable with. ;D