At the very early stages of a start-up (before you've even got a team together, much less secured any investment) there are loads of tools that can help you keep track of initial conversations.
Campfire is a fantastic tool for creating a forum or message board for your team to kick about ideas on.
(bought today by Twitter) is one of the simpler ways to start a blog; you populate it simply by sending emails to a given address.
allows you to create a shareable pinboard so you can visualise your inspiration.
And once your conversations with potential collaborators, partners and investors are underway,
is a great CRM tool to help you keep track of conversations you've had, with whom and what you need to follow up on.