I've been using TiddlyWiki for a few months now. It's a editable wiki page all contained within a single html file.
The idea is that you make notes (called tiddlers) and edit content via the html/js interface. When you hit save (or the autosave kicks in) it overwrites itself to include all your updates.
It doesn't require a web host or anything complex, just save the .html file on your hard drive and open it in your favourite browser. I have set the file as my homepage and put it in my dropbox so it syncs across all my PCs.
Alternatively, GStoGSto has pointed out that tiddlyspot.com provides free online hosting of tiddlywiki pages with public and private options.