Johnn Four of roleplayingtips.com swears by Milenix's Myinfo. http://www.milenix.com/
I haven't yet sprung for that one, but it's been on my list for a while. In the meantime, I've been using MS Binder, which comes with Office. You have to kind of hunt for it, though; it's not part of the default installation options. It's a little clunky, but it does allow you to keep several related documents together and switch between them relatively quickly. I generally keep several spreadsheets and Word docs, and a database if necessary.
I haven't yet sprung for that one, but it's been on my list for a while. In the meantime, I've been using MS Binder, which comes with Office. You have to kind of hunt for it, though; it's not part of the default installation options. It's a little clunky, but it does allow you to keep several related documents together and switch between them relatively quickly. I generally keep several spreadsheets and Word docs, and a database if necessary.