I found out about Evernote a few months ago, but I hadn't started using it until this week. I wish I had started earlier.
Evernote is free (there is a premium version with more functionality that is fee based) and allows you to capture notes in a variety of formats and then access it from anywhere via the web or a mobile application.
What's really cool about it is that it allows you to take a picture of something, upload it to Evernote, and it can search text in the photo. I love this because there are times when I don't have the time, or ambition, to copy something down, so I'll take a photo of it with my smart phone. Then I can send it to Evernote and search the text of the memo in the photo.
You can also enter notes manually and import notes from other applications. There is a desktop version for Windows and Mac, a mobile web version to use from any web enabled device, an iPhone application, and a Windows Mobile application. The desktop version syncs with the web version so that you can access your data anywhere you can access the internet.
It is a really great application. Check it out at www.evernote.com