/var/www/. Just make a symbolic link to your Dropbox folder in order to get this working:
$ cd /var/ $ mv www wwwOLD $ sudo ln -s /home/yourusername/Dropbox/foldername wwwYou will get a "forbidden" error if you do just this. In order to get it all working, you need to change the permissions on your Dropbox folder:
$ cd /home/username $ chmod 755 DropboxThis way any changes made in foldername on Dropbox can instantly be viewed in your browser.