Bitvise WinSSHD is an easy to use SSH server which includes Secure remote access via console (vt100, xterm and bvterm supported), Secure remote access via GUI (Remote Desktop or WinVNC required), Secure file transfer using SFTP and SCP (compatible with all major clients) and Secure TCP/IP connection tunneling (port forwarding). If you're worried about security or want to harden your existing setup, then adding SSH on top of your RDP connection is the way to go. By default RDP is not entirely secure because the encryption it provides is only half-way meaning that it does not encrypt usernames and passwords. With SSH, you can encrypt the entire connection!
There are other SSH server's on the market, but they are very complex to set up. WinSSHD is free for individual/personal use and requires license purchase when used in a commercial environment. You can download it at http://www.bitvise.com/winsshd