CraigB
10
I know that there is an empty folder left under program data and sometimes program files still has the avast folder left there but it is also empty, there are always the avast registry keys left under software in HKCU-HKLM\WOw6432Node and HKEY_USERS\S-1-5-21-1876683074-2874930434-696838539-1000\Software.
There are also HKEY_CLASSES_ROOT\avastsoundsfile, HKEY_CLASSES_ROOT\avastlicfile, HKEY_CLASSES_ROOT\avast, HKEY_CLASSES_ROOT.avastsounds and a few others but can not remember where they were now.
There are also the legacy files in control set incuding 1 and 2 that DavidR mentioned but these have to be removed manually.