May I suggest http://filehippo.com/download_malwarebytes_anti_malware/
And http://filehippo.com/download_superantispyware/
Neither one will conflict with avast! Please take a look at all the various signatures for more info on what to use.
And…don’t be afraid to ask questions.
AdAware has an anti-virus engine which will conflict with avast!
SpyBot S&D isn’t worth the time.