This extension allows you to set your own avatar dimensions for the avatar extension.
It adds a global configuration array which contains the available avatar sizes. This array can be changed update safe in your localconfig.php by setting $GLOBALS['avatar']['avatar_maxdims'] to an array of your preferred avatar sizes, e.g. $GLOBALS['avatar']['avatar_maxdims'] = array(32, 48, 64, 80, 100, 128, 256, 512);

avatarsizer is available in the TYPOlight Extension Repository for Download.