AWS Ubuntu Instance - User rights
Solution 1:
In the specific case of files for a web server, it's ok to simply give ownership of that directory to the ubuntu user.
sudo chown -R ubuntu:ubuntu /var/www
Then you can drop files there easily.
You might also find some useful information about the EC2 user setup on Ubuntu in this article I wrote a while back:
Using sudo, ssh, rsync on the Official Ubuntu Images for EC2
http://alestic.com/2009/04/ubuntu-ec2-sudo-ssh-rsync