Zoho Notebook is by far one of the best ways to jot online although it's potential goes far beyond simple annotation. Create unlimited online private or public pages and enjoy lot's of modules to add to your pages. Did I mentioned all this is for free?
Stikkit gathers phone numbers, addresses, birthdays, and other useful bits of information. As you write, Stikkit searches for appointments, To Do lists, people, bookmarks, and others. Then, like magic, it extracts and organizes the most important details for you.
Xiclets allows you to create and host xiclets (mini web pages) at the speed of light. Choose a name and password to your Xiclet and it becomes yours. Use the password to re-edit them any time you want.
Google Notebook is a fabulous free note taking service that allows you to create and share unlimited online notes. Access your notes from anywhere and any computer.
Notesphere is a very simple to use note organizer. It's a bit like cl1p.net but you can't share the notes. They can be read only by you.
cl1p.net is a free service that allows you to annotate and save your notes - like if you were using notepad - but online.