A desktop wiki like tool for keeping track of notes, phone numbers, and even has built in tools to use as your GTD system. It is cross platform running on Linux and Windows. With Dropbox you can keep your notes synced between all of your computers. You can even attach documents, files, and insert pictures too to keep all of your information in one place. Each note page is saved in plain text making it possible to edit the files with a normal text editor if you do not have Zim Wiki installed on a computer but have access to the files.
A recent interview with Getting Things Done productivity Author David Allen - If you are in need of organizing your "to-do" list, this is a great summary of his popular system
I have enjoyed this guy's blog for a few years. I got the Kindle version for on sale for $5.99 after the new year but haven't read it yet. The book is based on a productivity series he wrote last year that was very good. I'm looking forward to getting to it.