This plugin for ChatZilla shows you the changes made to a channel's topic.
=-= Nickname has changed the topic to “ChatZilla topic diff test”
=-= Nickname has changed the topic to “ChatZilla diff test”
=-= Nickname deleted "topic ".
=-= Nickname has changed the topic to “ChatZilla diff testing!”
=-= Nickname added "ing!".
=-= Nickname has changed the topic to “ChatZilla topic diffing”
=-= Nickname added "topic ", deleted " test", deleted "!".