After the disappointing discontinuation of Google Notebook, I've been testing a few different replacements, and I think I've settled on Evernote as by far my favorite.  I can't imagine anyone who does ANY amount of online research not using a tool like this. 

From their site, the list several great features:

On the web - Create, clip, and share notes on the web and see them everywhere There is an excellent Firefox extension too.  Definitely worth the install. 

Evernote on Mobile Phones -Take snapshots, read to-do lists, record audio whenever and wherever you like Evernote on Mac and PC -On your desktop - Search through all your notes, even find text within images, whether online or off The mobile phone application is cool.  If you're out an about, you can easily add notes or photos to Evernote, and they'll be on you computer when you next fire up the program.  Slick as snot.

Another really cool feature is that it recognizes text within images.  So if you've got a photo of a donut sign, and search on the word donut, it should find it.  Awesome. 

A few disappointments- The Free service has limitations, based on quantity of notes.  This is a pretty minor complaint, as the free limit seems relatively generous.  And anyone using the tool enough to hit those limits should be willing to pay a bit.  Bigger disappointment is that it lacks the easy collaboration tools that Google Notebook had.  It'd be awesome to be able to share notes with other Evernote users.   You can publish you notes, so others can see them, but there is not an easy way I see to allow others to share a common Notebook.  Hopefully Evernote will add this feature in the future.