I was just wondering what else I should be running on my computer (my os is Windows 7) besises avast Free Anti-Virus? My computer is running really slowly. I just noticed that I’m also still running Windows Defender. I think that this might be part of my problem. Please help!
you can turn off windows defender and install Malwarebytes
the PRO version have auto update and a protection module…a one time fee for a life time license 
http://www.malwarebytes.org/
OBS: was your computer delivered with a preinstalled AV ?
did you uninstall this or any previous used AV before installing avast?
If you need help, just follow this guide to Installing avast!
A lot of us use Super Anti-Spyware Free. http://filehippo.com/download_superantispyware/
Personally I prefer using a firewall with HIPS along with avast, MBAM and SAS. 