A customer recommended CrossLoop for remote desktop between Windows boxes - it works a treat. The key features which put it ahead of the competition (VNC, Citrix, RDP etc.) are:

• free (but not open source)
• tiny - quick to download
• tidy - it doesn't leave crap everywhere
• intuitive i.e. easy for a typical user to download and install
• simple and friendly - host/join, click to connect
• encrypted (it uses tightVNC for this)
• simple to share files
• excellent compression, works well on thin-ish connections
• it bloody works

Your mother/father/guardian/Luddite friend can use this!