I've been negotiating with about 12 individual creditors (I quite enjoy it, actually - the key is to be calm, very polite, very firm, and take no nonsense from them whatsoever) over the last few months, and have been using a web service called highrise to record who I've spoken to, what they said, when, what the agreed next action was, and reminders for what I need to do next.
Even better, the basic version is free. If you're not using a system (even a paper notebook) when dealing with these people, I recommend it. All of them have systems to record your interactions with them, and when they know you are doing the same, it discourages them from playing silly games.