Jill Duffy at PC Magazine quite likes online/offline notekeeper Evernote (as do we):
You can do a lot with the free version, and I would only recommend upgrading to Premium if you're so committed to Evernote that it will be your one-and-only note-making app. I like it better than Microsoft OneNote, and I really like that Evernote can integrate with Awesome Note (+Todo), another organizational app I use on my Apple iPhone. Choosing Evernote is not a hard commitment to make. Its leading feature is centralization—all your documents in one place, available any time—so it becomes more rewarding and more engaging the more you use it. If you want to get organized, Evernote Web deserves your attention.
-PC Magazine, April 5, 2011
One advantage Duffy doesn't emphasize is the multi-platform focus of Evernote, which has versions for iPhones and iPads, Androids and Blackberries as well as PCs and Macs. Less risk of lock-in (or lock-out) if you decide to make a switch in the future.