Regular note-taking is one of the most productive habits a person can practice. The ability to take notes online and access them anytime, from any location is priceless. The other great advantage of taking notes online is that it forces you to keep notes (decently) clear, (relatively) coherent, and (somewhat) systematic.
Here are some applications that you can try for note taking.

Listhings is an eco-friendly web app for storing notes.
The notes are automatically saved to Listhings database servers. When you’re a registered user, you can access your notes from anywhere, share them with anyone and collaborate in real-time. stores your text and keeps it synced between your work, home, and devices like the iPhone. Unlike manual syncing, merges your changes so you’ll never lose data. uses Google accounts for signing in.

If you are a Firefox user, then you can use Scribbly Firefox extension to take notes quickly right inside the browser. You can also create to-do lists or write any important points which strike during an online work. Download and install the extension. After restarting the browser, you’ll get the Scribbly icon on the bottom right of your Firefox browser.

You can start using this service by signing in with your Facebook, Google, Twitter or Friendfeed account. Notes can be taken online with a Google account to various pages you visit . This is not like a bookmark but basically leaving a small note. You can choose for the note to be saved as private or public. Public notes are visible to anyone visiting the page and being signed in with Stickr. You can follow up an article you have read online or even have a personal to-do list whenever you visit a particular website. Stickr allows you to download extensions and add-ons depending on the browser you use.

Google Sidewiki
Google has now come up with the service called SideWiki which literally allows someone using their Google account to leave a comment and look up comments for any website they visit. Google Sidewiki will be a part of Google Chrome directly instead of a toolbar in the future. Users with the old Google’s old toolbar for Firefox and IE can get the option to upgrade so they can avail of Sidewiki.
Users can share the comment using Email, Twitter and Facebook. The comments are ranked Useful or not and this is the way Google is planning to weed out the spam that very popular websites will attract. The highest ranked comments stay on the website. The lowest ranked find themselves at the bottom and probably out of sight.

NoteSync is a small utility that allows you to take notes fast and sync them with your Google docs account. It works using the Adobe Air platform and is a very light application. First advantage is an automatic sync to your Google Docs account every minute or when you wish. You can search notes and even the text inside them quickly. Connection to Google is HTTPS based and local storage is also encrypted. Lastly, all your notes can be found under the folder ‘NoteSync’ in Google Docs.

There are more note-taking applications on the net.

40 ways to take notes online (Marc and Angel blog)

Top ten online note taking applications (Mashable)

50 ways to take notes (Solution Watch)