Windows only: Face recognition software Blink lets you log in to Windows through your webcam-enabled computer. It also grabs a shot of everyone who successfully logs in, by face or by keyboard, so you know who's been up to what.
The login history is useful for seeing who's used your computer recently, as well as seeing anyone who's managed to look enough like you to break through the app's touted recognition algorithms. Food for thought: if you could somehow save the photos automatically to a folder, and have it synced to Dropbox, could you make your own home-brewed tracker for laptop thieves?
Blink claims to recognise you whether you change your haircut, grow a beard or switch out glasses for contacts. While we didn't try logging on with a picture of ourselves, a test involving dark sunglasses under "High Security" mode failed to log us in to Windows, which made us feel better.
Blink is freeware for Windows 32-bit systems only. What's your ideal, secure login idea for Windows? Does it involve faces, thumbprints, passwords or something else entirely? We'd like to hear your thoughts in the comments.